Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Before Tax Amount
(Loss) income, Before Tax Amount		$ 19,578	$ 15,676
Net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount
Net unrealized holding gains (losses) arising during the period		5,120	(6,338)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(1)	(10)
Total net unrealized gains (losses) on available-for-sale investment securities		5,119	(6,348)
Cash flow hedge derivative, Before Tax Amount
Net unrealized holding (losses) gains arising during the period		(168)	212
Less: reclassification adjustment for net losses realized in net income	[2]	(16)	20
Total net unrealized (losses) gains on interest rate swaps used in cash flow hedges		(184)	232
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	294	281
Accretion of prior service cost included in net periodic pension costs	[3]	(45)	(71)
Total defined benefit pension plans		249	210
Other comprehensive income, Before Tax Amount		5,184	(5,906)
Total comprehensive income (loss), Before Tax Amount		24,762	9,770
Tax Expense (Benefit)
Income tax expense		3,499	2,826
Net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)
Net unrealized holding gains (losses) arising during the period		1,075	(1,331)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	0	(2)
Total net unrealized gains (losses) on available-for-sale investment securities		1,075	(1,333)
Net unrealized losses on interest rate swaps used in cash flow hedges, Tax Expense (Benefit)
Net unrealized holding gains (losses) arising during the period		(36)	45
Less: reclassification adjustment for net losses realized in net income	[2]	(3)	4
Total net unrealized gains on interest rate swaps used in cash flow hedges		(39)	49
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs	[3]	62	59
Accretion of prior service cost included in net periodic pension costs	[3]	(9)	(15)
Total defined benefit pension plans		53	44
Other comprehensive income, Tax Expense (Benefit)		1,089	(1,240)
Total comprehensive income (loss), Tax Expense (Benefit)		4,588	1,586
Net of Tax Amount
Net income		16,079	12,850
Net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount
Net unrealized holding gains (losses) arising during the period		4,045	(5,007)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(1)	(8)
Total net unrealized gains (losses) on available-for-sale investment securities		4,044	(5,015)
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		(132)	167
Less: reclassification adjustment for net losses realized in net income	[2]	(13)	16
Total net unrealized (losses) gains on interest rate swaps used in cash flow hedges		(145)	183
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	232	222
Accretion of prior service cost included in net periodic pension costs	[3]	(36)	(56)
Total defined benefit pension plans		196	166
Other comprehensive income, Net of Tax Amount		4,095	(4,666)
Total comprehensive income (loss), Net of Tax Amount		$ 20,174	$ 8,184

[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.