Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustments out of AOCI [Abstract]
Net securities losses (gains)	$ 6,341	$ (1,867)	$ 644
Interest income	305,629	283,493	264,441
Other noninterest income	15,228	11,991	15,961
Other noninterest expense	19,597	20,308	17,294
Interest expense	38,626	25,914	22,506
Income tax expense (benefit)	24,436	46,010	40,392
Net Income	112,566	82,151	78,409
Total reclassifications, net of tax	4,617	1,131	2,524
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Income tax expense (benefit)	(1,827)	(120)	(677)
Net Income	5,483	198	1,061
Losses (Gains) on AFS Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Net securities losses (gains)	6,622	(1,869)	644
Amortization of Unrealized Gains Related to Securities Transfer [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Interest income	688	875	1,094
Impairment Write-Down of an Equity Security [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Other noninterest income	0	1,312	0
Net Unrealized (Gains) on Cash Flow Hedges Reclassified to Interest (Income) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Interest expense	(2,300)	(292)	69
Income tax expense (benefit)	575	113	(27)
Net Income	(1,725)	(179)	42
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Income tax expense (benefit)	(286)	(740)	(949)
Net Income	859	1,112	1,421
Amortization of Net Losses [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Other noninterest expense	1,054	1,755	2,395
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Other noninterest expense	$ 91	$ 97	$ (25)