Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) and the Related Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Securities available for sale and transferred securities, Before tax amount [Abstract]
Unrealized holding (losses) gains arising during the period, Before tax amount	$ 2,285	$ 35,343
Reclassification adjustment for net losses (gains) realized in net income, Before tax amount	0	310
Change in net unrealized holding loss on securities transferred to held to maturity, Before tax amount	1,232	2,724
Total securities available for sale and transferred securities, Before tax amount	3,517	38,377
Securities available for sale and transferred securities, Tax (expense) benefit [Abstract]
Unrealized holding (losses) gains arising during the period, Tax (expense) benefit	(874)	(13,518)
Reclassification adjustment for net gains realized in net income, Tax (expense) benefit	0	(119)
Change in net unrealized holding loss on securities transferred to held to maturity, Tax (expense) benefit	(471)	(1,042)
Total securities available for sale and transferred securities, Tax (expense) benefit	(1,345)	(14,679)
Securities available for sale and transferred securities, Net of tax amount [Abstract]
Unrealized holding (losses) gains arising during the period, net of tax amount	1,411	21,825
Reclassification adjustment for net losses (gains) realized in net income, net of tax amount	0	191
Change in net unrealized holding loss on securities transferred to held to maturity	761	1,682
Total securities available for sale and transferred securities, net of tax amount	2,172	23,698
Pension and other postretirement benefit plans, Before tax amount [Abstract]
Net change in prior service costs, before tax amount	63	62
Recognized net loss due to lump sum settlements, before tax amount	0	423
Change in net actuarial loss, before tax amount	787	882
Total pension and other postretirement benefit plans, before tax amount	850	1,367
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	0	(162)
Change in net actuarial loss, tax (expense) benefit	(301)	(337)
Total pension and other postretirement benefit plans, tax (expense) benefit	325	523
Pension and other postretirement benefit plans, Net of tax amount [Abstract]
Net change in prior service costs, net of tax amount	39	38
Recognized net loss due to lump sum settlements, net of tax amount	0	261
Change in net actuarial loss, net of tax amount	486	545
Total pension and other postretirement benefit plans, net of tax amount	525	844
Cash flow hedge derivatives, Before tax amount [Abstract]
Change in accumulated gain (loss) on effective cash flow hedge derivatives, before tax amount	57	(1,328)
Reclassification adjustment for loss realized in net income, before tax amount	99	160
Total cash flow hedge derivatives, before tax benefit	156	(1,168)
Total other comprehensive income (loss), Before tax amount	4,523	38,576
Cash flow hedge derivatives, Tax (expense) benefit [Abstract]
Change in accumulated gain (loss) on effective cash flow hedge derivatives , tax (expense) benefit	(22)	508
Reclassification adjustment for loss realized in net income, tax (expense) benefit	(38)	(61)
Total cash flow hedge derivatives, tax (expense) benefit	60	(447)
Total other comprehensive income (loss), Tax expense (benefit)	(1,730)	(14,755)
Cash flow hedge derivatives, Net of tax amount [Abstract]
Change in accumulated gain (loss) on effective cash flow hedge derivatives, net of tax amount	35	(820)
Reclassification adjustment for loss realized in net income, net of tax amount	61	99
Total cash flow hedge derivatives, net of tax amount	96	(721)
Total other comprehensive income (loss), net of tax amount	$ 2,793	$ 23,821