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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Adjustments to fair value included in earnings
Unrealized gain on investments at fair value	$ 4,714	$ 7,163	$ 22,190	$ 5,824
Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning			47,507	54,461
Proceeds from investments			(57,039)	(326)
Adjustments to fair value included in earnings
Unrealized gain on investments at fair value			22,228	5,829
Balance, ending	$ 12,696	$ 59,964	$ 12,696	$ 59,964