Realized and Net Change in Unrealized Gains (Losses) on Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Realized Gains	$ 2,495	$ 80	$ 5,082
Net Change in Unrealized Gains (Losses)	11,128	(4,079)	(6,309)
Total realized and net change in unrealized gains (losses) on other investments	$ 13,623	$ (3,999)	$ (1,227)