Stockholder's Equity - Shares of Common Stock Issued During 2014 Under Employee Stock Purchase Plan (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares available, Beginning balance		236,483	236,483
Shares issued during period (shares)	5,702	7,068
Shares available, Ending Balance	223,713		223,713
Shares issued during period (per share price)	$ 31.38	$ 29.62