Annual report pursuant to Section 13 and 15(d)

Equity - Schedule of Common Stock Public Offerings and ATM (Detail)

v3.6.0.2
Equity - Schedule of Common Stock Public Offerings and ATM (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Net proceeds from follow-on from public offering $ 177,294 $ 180,486 $ 129,351
5/4/2015 Closing Date [Member] | Public Offering [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date May 04, 2015    
Public offerings of common stock, Shares Issued 4,600    
Public offerings of common stock, Price Per Share $ 18.50    
Net proceeds from follow-on from public offering $ 82,000    
10/19/2015 Closing Date [Member] | Public Offering [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date Oct. 19, 2015    
Public offerings of common stock, Shares Issued 5,750    
Public offerings of common stock, Price Per Share $ 18.00    
Net proceeds from follow-on from public offering $ 99,000    
6/21/2016 Closing Date [Member] | Public Offering [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date Jun. 21, 2016    
Public offerings of common stock, Shares Issued 4,600    
Public offerings of common stock, Price Per Share $ 19.78    
Net proceeds from follow-on from public offering $ 91,000    
5/09/2016 to 6/30/2016 Closing Date [Member] | At the Market Offering [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings of common stock, Shares Issued 65    
Public offerings of common stock, Price Per Share $ 20.31    
Net proceeds from follow-on from public offering $ 1,000    
5/09/2016 to 6/30/2016 Closing Date [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date May 09, 2016    
5/09/2016 to 6/30/2016 Closing Date [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date Jun. 30, 2016    
11/09/2016 Closing Date [Member] | Public Offering [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date Nov. 09, 2016    
Public offerings of common stock, Shares Issued 4,025    
Public offerings of common stock, Price Per Share $ 19.28    
Net proceeds from follow-on from public offering $ 77,000    
13/12/2016 to 29/12/2016 Closing Date [Member] | At the Market Offering [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings of common stock, Shares Issued 407    
Public offerings of common stock, Price Per Share $ 19.47    
Net proceeds from follow-on from public offering $ 8,000    
13/12/2016 to 29/12/2016 Closing Date [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date Dec. 13, 2016    
13/12/2016 to 29/12/2016 Closing Date [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Public offerings and ATM offerings of common stock, Closing Date Dec. 29, 2016