Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,595,000	43,200,000	43,563,000	43,214,000
Net income available to common stockholders	$ 22,876	$ 20,001	$ 64,514	$ 58,801
Basic EPS (in dollars per share)	$ 0.52	$ 0.46	$ 1.48	$ 1.36
Diluted EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,595,000	43,200,000	43,563,000	43,214,000
Dilutive effect of common stock options and restricted stock (in shares)	320,000	362,000	329,000	366,000
Weighted average common shares and common share equivalents (in shares)	43,915,000	43,562,000	43,892,000	43,580,000
Net income available to common stockholders	$ 22,876	$ 20,001	$ 64,514	$ 58,801
Diluted EPS (in dollars per share)	$ 0.52	$ 0.46	$ 1.47	$ 1.35
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options excluded from calculation of diluted EPS (in shares)	3,250	0	3,014	36,865