Stockholders' Equity (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Class of Stock [Line Items]
Beginning Balance				$ 180,306,000					$ 180,306,000
Net income	1,081,000	2,745,000	4,505,000	6,286,000	4,256,000	3,893,000	5,525,000	4,448,000	14,617,000	18,122,000	13,242,000
Net income on derivative instruments, net of tax										182,000	(90,000)
Ending Balance	198,281,000				180,306,000				198,281,000	180,306,000
Common Stock
Class of Stock [Line Items]
Beginning Balance (in shares)				6,847,515				6,811,464	6,847,515	6,811,464	6,773,104
Beginning Balance				7,000				7,000	7,000	7,000	7,000
Common Stock issuance under Employee Stock Purchase Plan									9,578	8,551	9,865
Exercise of stock options									72,050	27,500	40,550
Issuance of Restricted Common Stock									35,000
Purchase of Treasury Stock (in shares)									(5,831)		(12,055)
Ending Balance (in shares)	6,958,312				6,847,515				6,958,312	6,847,515	6,811,464
Ending Balance	7,000				7,000				7,000	7,000	7,000
Additional Paid-in Capital
Class of Stock [Line Items]
Beginning Balance				43,720,000				41,341,000	43,720,000	41,341,000	38,776,000
Common Stock issuance under Employee Stock Purchase Plan									307,000	252,000	137,000
Exercise of stock options									1,301,000	375,000	466,000
Issuance of Restricted Common Stock									34,000
Share-based compensation									1,615,000	1,580,000	1,819,000
Tax benefit on share-based compensation									335,000	172,000	143,000
Ending Balance	47,312,000				43,720,000				47,312,000	43,720,000	41,341,000
Retained Earnings
Class of Stock [Line Items]
Beginning Balance				138,498,000				120,376,000	138,498,000	120,376,000	107,134,000
Net income									14,617,000	18,122,000	13,242,000
Ending Balance	153,115,000				138,498,000				153,115,000	138,498,000	120,376,000
Accumulated Other Comprehensive Income (Loss)
Class of Stock [Line Items]
Beginning Balance								(182,000)		(182,000)	(32,000)
Net income on derivative instruments, net of tax										182,000	(150,000)
Ending Balance											(182,000)
Treasury Stock
Class of Stock [Line Items]
Beginning Balance (in shares)				282,850					282,850		270,795
Beginning Balance				(1,919,000)					(1,919,000)		(1,659,000)
Purchase of Treasury Stock (in shares)									5,831		12,055
Purchase of Treasury Stock									(234,000)		(260,000)
Ending Balance (in shares)	288,681								288,681		282,850
Ending Balance	$ (2,153,000)								$ (2,153,000)		$ (1,919,000)