Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Accounting Policies [Abstract]
Income from continuing operations for calculating basic and diluted earnings per share					$ 26,941	$ 19,528	$ 16,015	$ 22,954	$ 60,710	$ 85,438	$ 84,479
Loss from discontinued operations					0	0	0	(272)	0	(272)	(633)
Net income	$ 19,410	$ 11,173	$ 13,339	$ 16,788	$ 26,941	$ 19,528	$ 16,015	$ 22,682	$ 60,710	$ 85,166	$ 83,846
Weighted-average common shares for calculating basic earnings per share									28,138	28,671	29,079
Stock options and nonvested awards									188	399	495
Weighted-average common shares for calculating diluted earnings per share	28,097	28,224	28,411	28,620	28,804	28,805	29,341	29,342	28,326	29,070	29,574
Income from continuing operations (basic) (in dollars per share)									$ 2.16	$ 2.98	$ 2.91
Loss from discontinued operations (basic) (in dollars per share)									0.00	(0.01)	(0.02)
Net income per basic share (in dollars per share)									2.16	2.97	2.89
Income from continuing operations (diluted) (in dollars per share)					$ 0.94	$ 0.68	$ 0.55	$ 0.78	2.14	2.94	2.86
Loss from discontinued operations (diluted) (in dollars per share)					0.00	0.00	0.00	(0.01)	0.00	(0.01)	(0.02)
Net income per diluted share (in dollars per share)	$ 0.69	$ 0.40	$ 0.47	$ 0.59	$ 0.94	$ 0.68	$ 0.55	$ 0.77	$ 2.14	$ 2.93	$ 2.84