Fair Value Measurements - Reconciliation of the beginning and ending balances of the Level 3 assets and liabilities (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, Calculation [Roll Forward]
Balance, Beginning	$ 31,373	$ 30,391	$ 34,421	$ 24,209
Purchases	5,108	5,239	5,108	10,538
Sales	(359)	(2,758)	(522)	(4,732)
Realized losses on sale	0	(129)	0	(129)
Unrealized gains (losses)	(639)	(397)	(3,524)	2,460
Balance, End	$ 35,483	$ 32,346	$ 35,483	$ 32,346