Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Before Tax Amount
(Loss) income, Before Tax Amount		$ 20,137	$ 4,548	$ 39,715	$ 20,224
Net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount
Net unrealized holding gains (losses) arising during the period		2,933	(1,911)	8,053	(8,249)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(7)	0	(8)	(10)
Total net unrealized gains (losses) on available-for-sale investment securities		2,926	(1,911)	8,045	(8,259)
Cash flow hedge derivative, Before Tax Amount
Net unrealized holding (losses) gains arising during the period		(263)	154	(431)	366
Less: reclassification adjustment for net losses realized in net income	[2]	(14)	6	(30)	26
Total net unrealized (losses) gains on interest rate swaps used in cash flow hedges		(277)	160	(461)	392
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	294	282	588	563
Accretion of prior service cost included in net periodic pension costs	[3]	(46)	(71)	(91)	(142)
Total defined benefit pension plans		248	211	497	421
Other comprehensive income, Before Tax Amount		2,897	(1,540)	8,081	(7,446)
Total comprehensive income (loss), Before Tax Amount		23,034	3,008	47,796	12,778
Tax Expense (Benefit)
Income tax expense		3,669	191	7,168	3,017
Net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)
Net unrealized holding gains (losses) arising during the period		616	(401)	1,691	(1,732)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(2)	0	(2)	(2)
Total net unrealized gains (losses) on available-for-sale investment securities		614	(401)	1,689	(1,734)
Net unrealized losses on interest rate swaps used in cash flow hedges, Tax Expense (Benefit)
Net unrealized holding (losses) gains arising during the period		(55)	32	(91)	77
Less: reclassification adjustment for net losses realized in net income	[2]	(3)	1	(6)	5
Total net unrealized (losses) gains on interest rate swaps used in cash flow hedges		(58)	33	(97)	82
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs	[3]	62	58	124	117
Accretion of prior service cost included in net periodic pension costs	[3]	(10)	(14)	(19)	(29)
Total defined benefit pension plans		52	44	105	88
Other comprehensive income, Tax Expense (Benefit)		608	(324)	1,697	(1,564)
Total comprehensive income (loss), Tax Expense (Benefit)		4,277	(133)	8,865	1,453
Net of Tax Amount
Net income		16,468	4,357	32,547	17,207
Net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount
Net unrealized holding gains (losses) arising during the period		2,317	(1,510)	6,362	(6,517)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(5)	0	(6)	(8)
Total net unrealized gains (losses) on available-for-sale investment securities		2,312	(1,510)	6,356	(6,525)
Total net unrealized gains (losses) on interest rate swaps used in cash flow hedges, Net of Tax Amount
Net unrealized holding (losses) gains arising during the period		(208)	122	(340)	289
Less: reclassification adjustment for net losses realized in net income	[2]	(11)	5	(24)	21
Total net unrealized (losses) gains on interest rate swaps used in cash flow hedges		(219)	127	(364)	310
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	232	224	464	446
Accretion of prior service cost included in net periodic pension costs	[3]	(36)	(57)	(72)	(113)
Total defined benefit pension plans		196	167	392	333
Other comprehensive income, Net of Tax Amount		2,289	(1,216)	6,384	(5,882)
Total comprehensive income (loss), Net of Tax Amount		$ 18,757	$ 3,141	$ 38,931	$ 11,325

[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.