Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,579,000	43,099,000	43,546,000	43,220,000
Net income available to common stockholders	$ 21,359	$ 19,909	$ 41,638	$ 38,800
Basic EPS (in dollars per share)	$ 0.49	$ 0.46	$ 0.96	$ 0.90
Diluted EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,579,000	43,009,000	43,546,000	43,220,000
Dilutive effect of common stock options and restricted stock (in shares)	322,000	354,000	340,000	364,000
Weighted average common shares and common share equivalents (in shares)	43,901,000	43,363,000	43,886,000	43,584,000
Net income available to common stockholders	$ 21,359	$ 19,909	$ 41,638	$ 38,800
Diluted EPS (in dollars per share)	$ 0.49	$ 0.46	$ 0.95	$ 0.89
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	33,179	1,144	25,139