Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,825,000	43,714,000	43,806,000	43,692,000
Net income available to common stockholders	$ 32,379	$ 29,807	$ 92,061	$ 83,914
Basic EPS (in dollars per share)	$ 0.74	$ 0.68	$ 2.10	$ 1.92
Diluted EPS [Abstract]
Weighted average common shares outstanding (in shares)	43,825,000	43,714,000	43,806,000	43,692,000
Dilutive effect of common stock options and restricted stock (in shares)	313,000	337,000	302,000	317,000
Weighted average common shares and common share equivalents (in shares)	44,138,000	44,051,000	44,108,000	44,009,000
Net income available to common stockholders	$ 32,379	$ 29,807	$ 92,061	$ 83,914
Diluted EPS (in dollars per share)	$ 0.73	$ 0.68	$ 2.09	$ 1.91
Stock Options [Member]
Earnings Per Share [Abstract]
Stock options excluded from calculation of diluted EPS (in shares)	1,500	1,500	1,500	1,500