Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustments out of AOCI [Abstract]
Net securities (gains) losses	$ (4,213)	$ 6,341	$ (1,867)
Interest income	311,555	305,629	283,493
Other noninterest income	18,853	15,228	11,991
Other noninterest expense	24,440	19,597	20,308
Interest expense	(55,979)	(38,626)	(25,914)
Income tax expense (benefit)	34,411	24,436	46,010
Net Income	121,021	112,566	82,151
Total reclassifications, net of tax	1,117	4,617	1,131
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)	(204)	(1,827)	(120)
Net Income	612	5,483	198
Losses (Gains) on AFS Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Net securities (gains) losses	79	6,622	(1,869)
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	737	688	875
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	0	1,312
Net Unrealized (Gains) on Cash Flow Hedges Reclassified to Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Interest expense	(2,012)	(2,300)	(292)
Income tax expense (benefit)	503	575	113
Net Income	(1,509)	(1,725)	(179)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Income tax expense (benefit)	(672)	(286)	(740)
Net Income	2,014	859	1,112
Amortization of Net Losses [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Other noninterest expense	2,593	1,054	1,755
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustments out of AOCI [Abstract]
Other noninterest expense	$ 93	$ 91	$ 97