Stock-Based Compensation - Summary of Weighted Average Grant-Date Fair Value of Common Stock Units and Share Awards Granted and Total Fair Value of Common Stock Units and Share Awards Vested (Detail) - Common Stock Awards [Member] - Non-Employee Director Fee Plan [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	32	36	37
Weighted average grant-date fair value	$ 24.70	$ 20.15	$ 16.01
Fair value of vested	$ 790	$ 630	$ 669