Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,663,000	43,513,000
Net income available to common stockholders	$ 25,986	$ 20,279
Basic EPS (in dollars per share)	$ 0.60	$ 0.47
Diluted EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,663,000	43,513,000
Dilutive effect of common stock options and restricted stock (in shares)	312,000	370,000
Weighted average common shares and common share equivalents (in shares)	43,975,000	43,883,000
Net income available to common stockholders	$ 25,986	$ 20,279
Diluted EPS (in dollars per share)	$ 0.59	$ 0.46
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options excluded from calculation of diluted EPS (in shares)	1,500	783