Stockholder's Equity - Shares of Common Stock Issued During 2013 Under Employee Stock Purchase Plan (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 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	9,600	10,385	8,845
Shares available, Ending Balance	282,417			282,417
Shares issued during period, Per share price	$ 18.60	$ 20.43	$ 20.24