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) - Nonvested Common Stock Share Awards [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	32	36
Weighted average grant-date fair value	$ 24.70	$ 20.15
Fair value of vested	$ 370	$ 310