Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income		$ 29,600	$ 34,950	$ 63,110	$ 57,805
Net income applicable to non-vested restricted shares		(240)	(336)	(551)	(570)
Net income applicable to common shares		$ 29,360	$ 34,614	$ 62,559	$ 57,235
Weighted-average common shares outstanding:
Weighted-average common shares outstanding (basic) (in Shares)		102,159	101,743	102,041	101,081
Dilutive effect of common stock equivalents (in Shares)		0	20	8	20
Weighted-average diluted common shares outstanding (in Shares)		102,159	101,763	102,049	101,101
Basic EPS (in dollars per share)		$ 0.29	$ 0.34	$ 0.61	$ 0.57
Diluted EPS (in dollars per share)		$ 0.29	$ 0.34	$ 0.61	$ 0.57
Anti-dilutive shares not included in the computation of diluted EPS (in Shares)	[1]	0	195	54	269

[1] This amount represents outstanding stock options for which the exercise price is greater than the average market price of the Company's common stock. The final outstanding stock options were exercised during the first quarter of 2018.