Accumulated Other Comprehensive Income (Loss) - Reclassifications (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Interest expense - subordinated debentures and term loans									$ (6,661)	$ (6,616)	$ (3,531)
Other expenses - salaries and employee benefits									(101,908)	(96,499)	(85,413)
Income tax expense	$ (4,418)	$ (6,557)	$ (8,856)	$ (5,834)	$ (5,638)	$ (5,980)	$ (5,888)	$ (4,617)	(25,665)	(22,123)	(15,884)
NET INCOME	$ 14,177	$ 17,067	$ 17,968	$ 16,172	$ 15,260	$ 16,122	$ 15,160	$ 13,620	65,384	60,162	44,530
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
NET INCOME									1,006	1,748	(1,438)
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									2,670	3,581	487
Income tax expense									(934)	(1,253)	(170)
NET INCOME									1,736	2,328	317
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]
Interest expense - subordinated debentures and term loans									(1,427)	(1,411)	(935)
Income tax expense									499	493	327
NET INCOME									(928)	(918)	(608)
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]
Other expenses - salaries and employee benefits									305	520	(1,765)
Income tax expense									(107)	(182)	618
NET INCOME									$ 198	$ 338	$ (1,147)