Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 20,405	$ 25,625	$ 27,122
Other comprehensive income (loss), net of tax:
Change in fair value of interest rate swap agreements	1,138	(1,977)	(2,372)
Total other comprehensive income (loss)	1,138	(1,977)	(2,372)
Comprehensive income	$ 21,543	$ 23,648	$ 24,750