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	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning	$ 12,561	$ 47,507
Proceeds from investment realizations	(3,609)	(57,039)
Transfers out of level 3	(20,745)
Adjustments to fair value included in earnings
Gain on investments at fair value	$ 11,793	22,093
Balance, ending		$ 12,561