Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Before Tax Amount
(Loss) income, Before Tax Amount		$ 18,168	$ 15,612	$ 38,392	$ 46,385
Net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount
Net unrealized holding (losses) gains arising during the period		(1,122)	1,030	(9,371)	4,082
Less: reclassification adjustment for net gains on sales realized in net income	[1]	0	(7)	(10)	(43)
Total net unrealized (losses) gains on available-for-sale investment securities		(1,122)	1,023	(9,381)	4,039
Cash flow hedge derivative, Before Tax Amount
Net unrealized holding gains (losses) arising during the period		79	(20)	445	(105)
Less: reclassification adjustment for net losses realized in net income	[2]	1	41	27	148
Total net unrealized gains on interest rate swaps used in cash flow hedges		80	21	472	43
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	281	320	844	918
Accretion of prior service cost included in net periodic pension costs	[3]	(70)	(71)	(212)	(212)
Total defined benefit pension plans		211	249	632	706
Other comprehensive income, Before Tax Amount		(831)	1,293	(8,277)	4,788
Total comprehensive income (loss), Before Tax Amount		17,337	16,905	30,115	51,173
Tax Expense (Benefit)
Income tax expense		3,204	4,416	6,221	12,555
Net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)
Net unrealized holding (losses) gains arising during the period		(236)	362	(1,968)	1,430
Less: reclassification adjustment for net gains on sales realized in net income	[1]	0	(2)	(2)	(15)
Total net unrealized (losses) gains on available-for-sale investment securities		(236)	360	(1,970)	1,415
Net unrealized losses on interest rate swaps used in cash flow hedges, Tax Expense (Benefit)
Net unrealized holding gains (losses) arising during the period		17	(7)	93	(37)
Less: reclassification adjustment for net losses realized in net income	[2]	0	14	6	52
Total net unrealized gains on interest rate swaps used in cash flow hedges		17	7	99	15
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs	[3]	60	112	177	321
Accretion of prior service cost included in net periodic pension costs	[3]	(15)	(25)	(44)	(74)
Total defined benefit pension plans		45	87	133	247
Other comprehensive income, Tax Expense (Benefit)		(174)	454	(1,738)	1,677
Total comprehensive income (loss), Tax Expense (Benefit)		3,030	4,870	4,483	14,232
Net of Tax Amount
Net income		14,964	11,196	32,171	33,830
Net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount
Net unrealized holding (losses) gains arising during the period		(886)	668	(7,403)	2,652
Less: reclassification adjustment for net gains on sales realized in net income	[1]	0	(5)	(8)	(28)
Total net unrealized (losses) gains on available-for-sale investment securities		(886)	663	(7,411)	2,624
Total net unrealized gains (losses) on interest rate swaps used in cash flow hedges, Net of Tax Amount
Net unrealized holding gains (losses) arising during the period		62	(13)	352	(68)
Less: reclassification adjustment for net losses realized in net income	[2]	1	27	21	96
Total net unrealized gains on interest rate swaps used in cash flow hedges		63	14	373	28
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	221	208	667	597
Accretion of prior service cost included in net periodic pension costs	[3]	(55)	(46)	(168)	(138)
Total defined benefit pension plans		166	162	499	459
Other comprehensive income, Net of Tax Amount		(657)	839	(6,539)	3,111
Total comprehensive income (loss), Net of Tax Amount		$ 14,307	$ 12,035	$ 25,632	$ 36,941

[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.