Fair Values - Reconciliation of Beginning and Ending Balances of Assets Measured at Fair Value on Recurring Basis Using Level 3 Inputs (Detail) - Level 3 [Member] - Recurring [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning	$ 12,561	$ 47,507
Proceeds from investment realizations	(2,406)	(15,038)
Adjustments to fair value included in earnings
Gain on investments at fair value	66	17,498
Balance, ending	$ 10,221	$ 49,967