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Fair Value Measurements - Assets Measured and Reported at Fair Value on Recurring Basis Using Significant Level 3 Inputs (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Balance at beginning of period $ 30,960 $ 28,895 $ 19,256
Unrealized gain 1,290 2,065 9,639
Proceeds from sale (32,250)    
Balance at end of period $ 0 $ 30,960 $ 28,895