Quarterly Financial Summary (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 78,625	$ 73,803	$ 76,745	$ 83,966	$ 85,912	$ 76,291	$ 80,263	$ 85,444	$ 313,139	$ 327,910	$ 350,020
Income from continuing operations	11,259	429	10,697	16,007	15,759	10,549	11,607	14,481	38,392	52,396	66,193
Net income	$ 6,893	$ 326	$ 6,596	$ 10,340	$ 9,791	$ 6,757	$ 7,073	$ 8,793	$ 24,155	$ 32,414	$ 40,877
Net income per common share:
Basic (in dollars per share)	$ 0.43	$ 0.02	$ 0.41	$ 0.64	$ 0.61	$ 0.41	$ 0.42	$ 0.51	$ 1.50	$ 1.94	$ 2.36
Diluted (in dollars per share)	$ 0.42	$ 0.02	$ 0.41	$ 0.64	$ 0.60	$ 0.41	$ 0.42	$ 0.51	$ 1.49	$ 1.93	$ 2.33