Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Available-for-Sale Securities (Detail)

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Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Balance, beginning of period     $ 27,273  
Transfers to / purchases of available-for-sale debt securities     20,486  
Balance, end of period $ 28,455   28,455  
Level 3 [Member]        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Balance, beginning of period 22,800   27,300  
Transfers to / purchases of available-for-sale debt securities 15,500 $ 83,500 20,500 $ 83,500
Payments on available-for-sale debt securities (1,000)   (8,600)  
Sale of available-for-sale debt securities (8,500) (20,700) (10,800) (20,700)
Gains on debt securities transferred to available for sale   5,000   5,000
Gains on debt securities recorded in earnings 500   800  
Losses on debt securities recorded in OCI (800) (200) (700) (200)
Balance, end of period $ 28,500 $ 67,600 $ 28,500 $ 67,600