Fair Values - Reconciliation of Beginning and Ending Balances of Assets Measured at Fair Value on Recurring Basis Using Level 3 Inputs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Adjustments to fair value included in earnings
Unrealized gain on investments at fair value	$ (82)	$ 1,780	$ 22,108	$ 7,604
Level 3 [Member] | Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning			47,507	54,461
Proceeds from investment realizations			(57,039)	(19,781)
Adjustments to fair value included in earnings
Unrealized gain on investments at fair value			22,228	7,616
Balance, ending	$ 12,696	$ 42,296	$ 12,696	$ 42,296