Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Net securities gains	$ 4,036	$ 412	$ 4,024	$ 575
Interest income (expense)	78,054	77,527	234,372	226,754
Other noninterest expense	8,374	4,577	18,130	13,324
Income tax expense (benefit)	9,322	8,578	26,245	23,699
Net income	32,379	29,807	92,061	83,914
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	335	(138)	516	(96)
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)	(42)	(42)	(159)	(133)
Net income	128	126	476	400
Gains (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	(20)	0	79	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)	190	168	556	533
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)	(395)	(638)	(1,932)	(1,537)
Income tax expense (benefit)	98	159	483	384
Net income	(297)	(479)	(1,449)	(1,153)
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)	(168)	(71)	(496)	(219)
Net income	504	215	1,489	657
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	649	263	1,916	809
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	$ 23	$ 23	$ 69	$ 67