Stockholder's Equity - Shares of Common Stock Issued During 2013 Under Employee Stock Purchase Plan (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2013
Shares Held In Employee Stock Purchase Plan [Abstract]
Shares available, Beginning balance		61,247	61,247
Additional shares authorized for issuance			250,000
Shares issued during period	10,385	8,845
Shares available, Ending Balance	292,017		292,017
Shares issued during period, Per share price	$ 20.43	$ 20.24