Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income		$ 53,352	$ 38,235	$ 116,462	$ 96,040
Net income applicable to non-vested restricted shares		(441)	(340)	(992)	(910)
Net income applicable to common shares		$ 52,911	$ 37,895	$ 115,470	$ 95,130
Weighted-average common shares outstanding:
Weighted-average common shares outstanding (basic) (in Shares)		102,178	101,752	102,087	101,307
Dilutive effect of common stock equivalents (in Shares)		0	20	5	20
Weighted-average diluted common shares outstanding (in Shares)		102,178	101,772	102,092	101,327
Basic EPS (in dollars per share)		$ 0.52	$ 0.37	$ 1.13	$ 0.94
Diluted EPS (in dollars per share)		$ 0.52	$ 0.37	$ 1.13	$ 0.94
Anti-dilutive shares not included in the computation of diluted EPS (in Shares)	[1]	0	190	36	242

[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.