Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) and the Related Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Securities available for sale and transferred securities, Before tax amount [Abstract]
Unrealized holding (losses) gains arising during the period, Before tax amount	$ (12,657)	$ 17,872	$ 32,057	$ 13,718
Reclassification adjustment for net losses realized in net income, Before tax amount			310
Change in net unrealized holding loss on securities transferred to held to maturity, Before tax amount	2,677	1,678	8,374	4,747
Total securities available for sale and transferred securities, Before tax amount	(9,980)	19,550	40,741	18,465
Securities available for sale and transferred securities, Tax (expense) benefit [Abstract]
Unrealized holding (losses) gains arising during the period, Tax (expense) benefit	4,841	(6,837)	(12,261)	(5,248)
Reclassification adjustment for net gains realized in net income, Tax (expense) benefit			(119)
Change in net unrealized holding loss on securities transferred to held to maturity, Tax (expense) benefit	(1,024)	(642)	(3,203)	(1,816)
Total securities available for sale and transferred securities, Tax (expense) benefit	3,817	(7,479)	(15,583)	(7,064)
Securities available for sale and transferred securities, Net of tax amount [Abstract]
Net unrealized holding (losses) gains on AFS Securities, net of tax at date of transfer	(7,816)	11,035	19,796	8,470
Less: adjustment for net losses realized in net income	0	0	191	0
Change in net unrealized holding loss on securities transferred to held to maturity, after tax income (expense)	1,653	1,036	5,171	2,931
Total securities available for sale and transferred securities, after tax income (expense)	(6,163)	12,071	25,158	11,401
Pension and other postretirement benefit plans, Before tax amount [Abstract]
Net change in prior service costs, before tax amount	63	63	188	188
Recognized net loss due to lump sum settlements, before tax amount	463	603	3,134	1,499
Change in net actuarial loss, before tax amount	928	1,216	2,684	3,653
Reclassification related to net losses realized in net income, before tax amount	1,454	1,882	6,006	5,340
Pension and other postretirement benefit plans, Tax (expense) benefit [Abstract]
Net change in prior service costs, tax (expense) benefit	(24)	(24)	(72)	(72)
Recognized net loss due to lump sum settlements, tax (expense) benefit	(177)	(230)	(1,199)	(573)
Change in net actuarial loss, tax (expense) benefit	(355)	(465)	(1,026)	(1,397)
Reclassification related to net losses realized in net income, tax (expense) benefit	(556)	(719)	(2,297)	(2,042)
Pension and other postretirement benefit plans, Net of tax amount [Abstract]
Net change in prior service costs	39	39	116	116
Recognized net loss due to lump sum settlements, after tax income (expense)	286	373	1,935	926
Change in net actuarial loss, after tax income (expense)	573	751	1,658	2,256
Reclassification related to net losses realized in net income, after tax income (expense)	898	1,163	3,709	3,298
Cash flow hedge derivatives, Before tax amount [Abstract]
Change in accumulated loss on effective cash flow hedge derivatives, before tax amount	417	(1,216)	(1,360)	(1,919)
Reclassification adjustment for loss realized in net income, before tax amount	157	211	473	632
Total cash flow hedge derivatives, before tax benefit	574	(1,005)	(887)	(1,287)
Total other comprehensive (loss) income, Before tax amount	(7,952)	20,427	45,860	22,518
Cash flow hedge derivatives, Tax (expense) benefit [Abstract]
Change in accumulated loss on effective cash flow hedge derivatives, tax (expense) benefit	(160)	465	520	734
Reclassification adjustment for loss realized in net income, tax (expense) benefit	(60)	(81)	(181)	(242)
Total cash flow hedge derivatives, tax (expense) benefit	(220)	384	339	492
Total other comprehensive (loss) income, Tax expense (benefit)	3,041	(7,814)	(17,541)	(8,614)
Cash flow hedge derivatives, Net of tax amount [Abstract]
Change in the accumulated loss on effective cash flow hedge derivatives, after tax amount	257	(751)	(840)	(1,185)
Less: adjustment for loss realized in net income	97	130	292	390
Total cash flow hedge derivatives, after tax amount	354	(621)	(548)	(795)
Total other comprehensive (loss) income, Net of tax	$ (4,911)	$ 12,613	$ 28,319	$ 13,904