Schedule of Investments in Term Deposits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Cost	$ 6,598	$ 413,566	$ 466,625
Maturities of term deposits	621,824	486,651	445,717
Purchases of term deposits	$ 223,904	$ 446,768	$ 583,341