Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Before Tax Amount
Income (loss), before tax amount		$ 23,197	$ 21,444	$ 25,250	$ 61,159
Net unrealized gains (losses) on available-for-sale investment securities, before tax amount
Other comprehensive income (loss), securities, available-for-sale, unrealized holding gain (loss) arising during period, before tax		726	(219)	2,930	7,834
Recovery of provision for credit losses, before tax		(163)
Provision for credit losses, before tax				392
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(57)	(33)	(817)	(41)
Other comprehensive income (loss), securities, available-for-sale, adjustment, before tax		506	(252)	2,505	7,793
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, before tax amount
Net unrealized holding gains (losses) arising during the period		5	(68)	(554)	(499)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	78	(4)	176	(34)
Other comprehensive income (loss), derivatives qualifying as hedges, before tax		83	(72)	(378)	(533)
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	307	294	901	882
Accretion of prior service cost included in net periodic pension costs	[3]	0	(45)	0	(136)
Total defined benefit pension plans		307	249	901	746
Other comprehensive income (loss), before tax amount		896	(75)	3,028	8,006
Total comprehensive income (loss), before tax amount		24,093	21,369	28,278	69,165
Tax Expense (Benefit)
Income tax expense		5,078	3,782	4,208	10,950
Net unrealized gains (losses) on available-for-sale investment securities, tax expense (benefit)
Other comprehensive income (loss), securities, available-for-sale, unrealized holding gain (loss) arising during period, tax		153	(46)	615	1,645
Recovery of provision for credit losses, tax		(35)
Provision for credit losses, tax				82
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(12)	(7)	(172)	(9)
Total net unrealized gains (losses) on available-for-sale investment securities		106	(53)	525	1,636
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, tax expense (benefit)
Other comprehensive income (loss), unrealized gain (loss) on derivatives arising during period, tax		2	(14)	(116)	(105)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	16	(1)	37	(7)
Other comprehensive income (loss), derivatives qualifying as hedges, tax		18	(15)	(79)	(112)
Defined benefit pension plans, tax expense (benefit)
Amortization of net actuarial loss included in net periodic pension costs	[3]	65	62	189	186
Accretion of prior service cost included in net periodic pension costs	[3]	0	(10)	0	(29)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, tax		65	52	189	157
Other comprehensive income (loss), tax expense (benefit)		189	(16)	635	1,681
Total comprehensive income (loss), tax expense (benefit)		5,267	3,766	4,843	12,631
Net of Tax Amount
Net income		18,119	17,662	21,042	50,209
Net unrealized gains (losses) on available-for-sale investment securities, net of tax amount
Net unrealized holding gains (losses) arising during the period		573	(173)	2,315	6,189
Recovery of provision for credit losses, after tax		(128)
Provision for credit losses, after tax				310
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(45)	(26)	(645)	(32)
Other comprehensive income (loss), securities, available-for-sale, adjustment, after tax		400	(199)	1,980	6,157
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, net of tax amount
Other comprehensive income (loss), unrealized gain (loss) on derivatives arising during period, net of tax		3	(54)	(438)	(394)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	62	(3)	139	(27)
Total net unrealized gains (losses) on interest rate swaps used in cash flow hedges		65	(57)	(299)	(421)
Defined benefit pension plans, net of tax amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	242	232	712	696
Accretion of prior service cost included in net periodic pension costs	[3]	0	(35)	0	(107)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, after tax		242	197	712	589
Other comprehensive income (loss), net of tax amount		707	(59)	2,393	6,325
Total comprehensive income (loss), net of tax amount		$ 18,826	$ 17,603	$ 23,435	$ 56,534

[1] (1) Included in net gain on sales of investment securities on the consolidated statements of income (before tax amount).

[2] (2) Included in interest expense on deposits on the consolidated statements of income (before tax amount).

[3] (3) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (before tax amount). See Note 8, "Retirement Plans and Other Postretirement Benefits" for additional details.