Other Comprehensive Income (Loss) - Tax effects of components in other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Before Tax
Other comprehensive income (loss)	$ 8,179	$ 5,697	$ 19,664	$ 14,082
Tax Effect
Other comprehensive income (loss)	(1,721)	(1,196)	(4,136)	(2,956)
After Tax
Total other comprehensive income	6,458	4,501	15,528	11,126
Unrealized Gains on Debt Securities Available for Sale
Before Tax
Other comprehensive income (loss), before reclassifications	8,041	17,829	32,425	29,595
Other comprehensive income (loss)	8,039	18,166	32,800	30,071
Tax Effect
Other comprehensive income (loss), before reclassifications	(1,689)	(3,737)	(6,806)	(6,208)
Other comprehensive income (loss)	(1,689)	(3,816)	(6,888)	(6,316)
After Tax
Other comprehensive income (loss), before reclassifications	6,352	14,092	25,619	23,387
Total other comprehensive income	6,350	14,350	25,912	23,755
AOCI, Accumulated Gain (Loss), Debt Securities Available-for-sale, Accretion Of Unrealized Gains (Losses), Parent
Before Tax
Reclassification from AOCI, current period	(2)	(2)	5	11
Tax Effect
Reclassification from AOCI, current period	0	0	(1)	(3)
After Tax
Reclassification from AOCI, current period	(2)	(2)	4	8
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Other Reclassifications, Parent
Before Tax
Reclassification from AOCI, current period	0	339	370	465
Tax Effect
Reclassification from AOCI, current period	0	(79)	(81)	(105)
After Tax
Reclassification from AOCI, current period	0	260	289	360
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Before Tax
Other comprehensive income (loss), before reclassifications	(945)	(5,920)	(15,306)	(9,440)
Tax Effect
Other comprehensive income (loss), before reclassifications	195	1,244	3,207	1,984
After Tax
Other comprehensive income (loss), before reclassifications	(750)	(4,676)	(12,099)	(7,456)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Before Tax
Reclassification from AOCI, current period	(14)	(14)	(28)	(28)
Tax Effect
Reclassification from AOCI, current period	3	3	6	6
After Tax
Reclassification from AOCI, current period	(11)	(11)	(22)	(22)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Before Tax
Reclassification from AOCI, current period	(1,071)	(925)	(2,142)	(1,849)
Tax Effect
Reclassification from AOCI, current period	226	194	450	388
After Tax
Reclassification from AOCI, current period	(845)	(731)	(1,692)	(1,461)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Before Tax
Other comprehensive income (loss), before reclassifications	2,170	(5,610)	4,340	(4,672)
Other comprehensive income (loss)	1,085	(6,549)	2,170	(6,549)
Tax Effect
Other comprehensive income (loss), before reclassifications	(456)	1,179	(911)	982
Other comprehensive income (loss)	(227)	1,376	(455)	1,376
After Tax
Other comprehensive income (loss), before reclassifications	1,714	(4,431)	3,429	(3,690)
Total other comprehensive income	$ 858	$ (5,173)	$ 1,715	$ (5,173)