Other Comprehensive Income (Loss) - Tax Effects of Components in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Before Tax
Other comprehensive income (loss)	$ (43,955)	$ 6,768	$ (24,291)	$ 20,850
Tax Effect
Other comprehensive income (loss)	9,233	(1,421)	5,097	(4,377)
After Tax
Total other comprehensive income (loss)	(34,722)	5,347	(19,194)	16,473
Unrealized Gains on Debt Securities Available for Sale
Before Tax
Other comprehensive income (loss), before reclassifications	(3,688)	6,186	28,736	35,781
Other comprehensive income (loss)	(3,692)	7,444	29,107	37,515
Tax Effect
Other comprehensive income (loss), before reclassifications	775	(1,271)	(6,031)	(7,479)
Other comprehensive income (loss)	775	(1,562)	(6,112)	(7,878)
After Tax
Other comprehensive income (loss), before reclassifications	(2,913)	4,915	22,705	28,302
Total other comprehensive income (loss)	(2,917)	5,882	22,995	29,637
AOCI, Accumulated Gain (Loss), Debt Securities Available-for-sale, Accretion Of Unrealized Gains (Losses), Parent
Before Tax
Reclassification from AOCI, current period	(4)	2	1	13
Tax Effect
Reclassification from AOCI, current period	0	0	0	(3)
After Tax
Reclassification from AOCI, current period	(4)	2	1	10
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Other Reclassifications, Parent
Before Tax
Reclassification from AOCI, current period	0	1,256	370	1,721
Tax Effect
Reclassification from AOCI, current period	0	(291)	(81)	(396)
After Tax
Reclassification from AOCI, current period	0	965	289	1,325
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Before Tax
Other comprehensive income (loss), before reclassifications	2,256	(1,619)	(13,050)	(11,059)
Tax Effect
Other comprehensive income (loss), before reclassifications	(471)	340	2,736	2,324
After Tax
Other comprehensive income (loss), before reclassifications	1,785	(1,279)	(10,314)	(8,735)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Before Tax
Reclassification from AOCI, current period	(14)	(14)	(42)	(42)
Tax Effect
Reclassification from AOCI, current period	3	3	10	9
After Tax
Reclassification from AOCI, current period	(11)	(11)	(32)	(33)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Before Tax
Reclassification from AOCI, current period	(1,071)	(930)	(3,213)	(2,779)
Tax Effect
Reclassification from AOCI, current period	225	195	674	583
After Tax
Reclassification from AOCI, current period	(846)	(735)	(2,539)	(2,196)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Before Tax
Other comprehensive income (loss), before reclassifications	(41,434)	1,887	(37,093)	(2,785)
Other comprehensive income (loss)	(42,519)	943	(40,348)	(5,606)
Tax Effect
Other comprehensive income (loss), before reclassifications	8,701	(397)	7,789	585
Other comprehensive income (loss)	8,929	(199)	8,473	1,177
After Tax
Other comprehensive income (loss), before reclassifications	(32,733)	1,490	(29,304)	(2,200)
Total other comprehensive income (loss)	$ (33,590)	$ 744	$ (31,875)	$ (4,429)