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	9 Months Ended
	Sep. 30, 2016	Sep. 30, 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)	(57,039)
Transfers out of level 3	(20,745)
Adjustments to fair value included in earnings
Gain on investments at fair value	11,790	22,228
Balance, ending	$ 1,200	$ 12,696