Accumulated Other Comprehensive Income (Loss) - Reclassifications (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Other income - net realized gains on sales of available for sale securities									$ 3,389	$ 2,670	$ 3,581
Income tax expense	$ (7,850)	$ (7,469)	$ (6,716)	$ (5,574)	$ (4,418)	$ (6,557)	$ (8,856)	$ (5,834)	(27,609)	(25,665)	(22,123)
Interest expense - subordinated debentures and term loans									(7,185)	(6,661)	(6,616)
Other expenses - salaries and employee benefits									(102,552)	(101,908)	(96,499)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 22,293	$ 21,059	$ 20,006	$ 17,693	$ 14,177	$ 17,067	$ 17,968	$ 16,172	81,051	65,384	60,162
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									2,422	1,006	1,748
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Unrealized gains (losses) on available for sale securities
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Other income - net realized gains on sales of available for sale securities									3,389	2,670	3,581
Income tax expense									(1,186)	(934)	(1,253)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									2,203	1,736	2,328
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Unrealized gains (losses) on cash flow hedges
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense									437	499	493
Interest expense - subordinated debentures and term loans									(1,250)	(1,427)	(1,411)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									(813)	(928)	(918)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Unrealized gains (losses) on defined benefit plans
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense									(556)	(107)	(182)
Other expenses - salaries and employee benefits									1,588	305	520
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									$ 1,032	$ 198	$ 338