CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 73,447	$ 105,333	$ 107,498
Other comprehensive income (loss), before tax expense (benefit):
Unrealized holding gains on securities arising during the period	19,981	20,625	2,783
Less: reclassification adjustment for gains on securities included in net income	(70)	(22)	(8,102)
Unrealized holding (losses) gains on derivatives arising during the period	(4,467)	935	326
Reclassification adjustment for losses on derivatives included in net income	0	0	10
Unrealized (losses) gains for postretirement obligations:
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Reclassification Adjustment, before Tax	(537)	0	0
Net (loss) gain	(155)	(121)	144
Total other comprehensive income (loss), before income tax expense (benefit)	14,752	21,417	(4,839)
Income tax expense (benefit) related to items of other comprehensive income (loss)	3,098	4,497	(1,015)
Comprehensive Income	$ 85,101	$ 122,253	$ 103,674