Earnings Per Common Share - Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income		$ 98,387	$ 92,349	$ 82,064
Net income applicable to non-vested restricted shares		(916)	(1,043)	(882)
Net income applicable to common shares		$ 97,471	$ 91,306	$ 81,182
Weighted-average common shares outstanding:
Weighted-average common shares outstanding (basic) (in shares)		101,423	79,797	77,059
Dilutive effect of common stock equivalents (in shares)		20	13	13
Weighted-average diluted common shares outstanding (in shares)		101,443	79,810	77,072
Basic EPS (in dollars per share)		$ 0.96	$ 1.14	$ 1.05
Diluted EPS (in dollars per share)		$ 0.96	$ 1.14	$ 1.05
Anti-dilutive shares not included in the computation of diluted EPS (in shares)	[1]	229	494	800

[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.