Stock Option Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total intrinsic value of stock options exercised	$ 1	$ 972	$ 1,535
Total fair value of share awards vested	$ 26,892	$ 21,673	$ 31,672