Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Quarterly Financial Information [Line Items]
Revenues	$ 271,184	$ 269,861	$ 276,488	$ 244,148	$ 250,979	$ 248,473	$ 228,877	$ 215,638	$ 1,061,681	$ 943,967	$ 902,729
Gross profit	32,611	28,620	31,736	29,374	42,082	32,724	30,528	27,080	122,341	132,414	124,877
Net income	$ 5,881	$ 6,175	$ 8,074	$ 7,172	$ 14,127	$ 8,404	$ 7,741	$ 6,272	$ 27,302	$ 36,544	$ 34,759
Basic earnings per share (in dollars per share)	$ 0.29	$ 0.3	$ 0.39	$ 0.35	$ 0.68	$ 0.4	$ 0.36	$ 0.3	$ 1.33	$ 1.73	$ 1.65
Diluted earnings per share (in dollars per share)	$ 0.29	$ 0.29	$ 0.38	$ 0.34	$ 0.66	$ 0.39	$ 0.36	$ 0.29	$ 1.30	$ 1.69	$ 1.61