Annual report pursuant to Section 13 and 15(d)

Credit Facilities - Schedule of Additional Detail on Credit Facility (Detail)

v3.8.0.1
Credit Facilities - Schedule of Additional Detail on Credit Facility (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Line of Credit Facility [Line Items]    
Outstanding balance $ 69,922 $ 283,346
Senior Secured Revolving Credit Facility [Member]    
Line of Credit Facility [Line Items]    
Outstanding balance 70,000 283,000
Value of collateral pledged to credit facility $ 252,000 $ 471,000
Weighted average short-term borrowing rate 3.00% 2.30%