Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) and the Related Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Securities available for sale and transferred securities, Before tax amount [Abstract]
Unrealized holding (losses) gains arising during the period, Before tax amount	$ 35,343	$ 18,438
Reclassification adjustment for net losses realized in net income, Before tax amount	310	0
Change in net unrealized holding loss on securities transferred to held to maturity, Before tax amount	2,724	1,415
Total securities available for sale and transferred securities, Before tax amount	38,377	19,853
Securities available for sale and transferred securities, Tax (expense) benefit [Abstract]
Unrealized holding losses (gains) arising during the period, Tax (expense) benefit	(13,518)	(7,052)
Reclassification adjustment for net gains realized in net income, Tax (expense) benefit	(119)	0
Change in net unrealized holding loss on securities transferred to held to maturity, Tax (expense) benefit	(1,042)	(541)
Total securities available for sale and transferred securities, Tax (expense) benefit	(14,679)	(7,593)
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	21,825	11,386
Less: adjustment for net losses realized in net income	191	0
Change in net unrealized holding loss on securities transferred to held to maturity, after tax income (expense)	1,682	874
Total securities available for sale and transferred securities, after tax income (expense)	23,698	12,260
Pension and other postretirement benefit plans, Before tax amount [Abstract]
Net change in prior service costs, before tax amount	62	63
Recognized net loss due to lump sum settlements, before tax amount	423	417
Change in net actuarial loss, before tax amount	882	1,220
Total pension and other postretirement benefit plans, before tax amount	1,367	1,700
Pension and other postretirement benefit plans, Tax (expense) benefit [Abstract]
Net change in prior service costs, tax (expense) benefit	(24)	(24)
Recognized net loss due to lump sum settlements, tax (expense) benefit	(162)	(160)
Change in net actuarial loss, tax (expense) benefit	(337)	(466)
Total pension and other postretirement benefit plans, tax (expense) benefit	(523)	(650)
Pension and other postretirement benefit plans, Net of tax amount [Abstract]
Net change in prior service costs	38	39
Recognized net loss due to lump sum settlements, after tax income (expense)	261	257
Change in net actuarial loss, after tax income (expense)	545	754
Total pension and other postretirement benefit plans, after tax income (expense)	844	1,050
Cash flow hedge derivatives, Before tax amount [Abstract]
Change in accumulated gain (loss) on effective cash flow hedge derivatives, before tax amount	(1,328)	(985)
Reclassification adjustment for loss realized in net income, before tax amount	160	211
Total cash flow hedge derivatives, before tax benefit	(1,168)	(774)
Total other comprehensive income (loss), Before tax amount	38,576	20,779
Cash flow hedge derivatives, Tax (expense) benefit [Abstract]
Change in accumulated gain (loss) on effective cash flow hedge derivatives, tax (expense) benefit	508	377
Reclassification adjustment for loss realized in net income, tax (expense) benefit	(61)	(81)
Total cash flow hedge derivatives, tax (expense) benefit	447	296
Total other comprehensive income (loss), Tax expense (benefit)	(14,755)	(7,947)
Cash flow hedge derivatives, Net of tax amount [Abstract]
Change in the accumulated gain (loss) on effective cash flow hedge derivatives, after tax amount	(820)	(608)
Less: adjustment for loss realized in net income	99	130
Total cash flow hedge derivatives, after tax amount	(721)	(478)
Total other comprehensive income (loss), Net of tax	$ 23,821	$ 12,832