Financial Instruments - Financial Instruments Held for Investment - Designated as Trading (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Realized Or Unrealized Gain Loss On Trading Securities [Abstract]
Net (loss) gains recognized on trading securities	$ (1,442)	$ 3,630	$ 1,213
Less: Net loss (gains) recognized on trading securities sold during the period	933	(3,732)	(261)
Unrealized (losses) gains recognized on trading securities still held at the reporting date	$ (509)	$ (102)	$ 952