Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Net securities gains	$ (69)	$ 91	$ (12)	$ 163
Interest income (expense)	78,627	75,741	156,318	149,227
Other noninterest expense	4,630	4,332	9,756	8,747
Income tax expense (benefit)	8,805	8,112	16,923	15,121
Net income	30,555	28,121	59,682	54,107
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	89	(51)	181	42
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)	(50)	(44)	(117)	(91)
Net income	149	133	348	274
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)	199	177	366	365
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)	(738)	(540)	(1,537)	(899)
Income tax expense (benefit)	185	135	385	225
Net income	(553)	(405)	(1,152)	(674)
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)	(328)	(148)
Net income	493	221	985	442
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	633	273	1,267	546
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	$ 24	$ 22	$ 46	$ 44