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Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Net securities gains	$ 57	$ 72
Interest income (expense)	77,691	73,486
Other noninterest expense	5,126	4,415
Income tax expense (benefit)	8,118	7,009
Net income	29,127	25,986
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Total reclassifications during the period, net of tax	92	93
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Income tax expense (benefit)	(67)	(47)
Net income	199	141
Losses on AFS Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Net securities gains	99	0
Amortization of Unrealized Gains Related to Securities Transfer [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Interest income (expense)	167	188
Net Unrealized (Gains) on Cash Flow hedges Reclassified to Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Interest income (expense)	(799)	(359)
Income tax expense (benefit)	200	90
Net income	(599)	(269)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Income tax expense (benefit)	(164)	(74)
Net income	492	221
Amortization of Net Losses [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Other noninterest expense	634	273
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Other noninterest expense	$ 22	$ 22

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