Stock-Based Compensation - Summary of Weighted Average Grant-Date Fair Value of Common Stock Awarded and Cash Used to Settle Company's Obligation under Deferred Compensation (Detail) - Common Stock [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	6	8
Weighted average grant-date fair value	$ 24.69	$ 20.43
Fair value of vested	$ 169	$ 146
Cash used to settle the obligation	$ 65	$ 21