Accumulated Other Comprehensive Loss (Changes in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		$ 2,668,749	$ 2,581,526	$ 1,015,974
Cumulative effect adjustment of change in accounting policy, net of tax impact	[1]		1,339	3,659
Other comprehensive income (loss) before reclassifications		(24,658)	12,054	(12,399)
Amounts reclassified from accumulated other comprehensive income (loss)		(10,613)	7,002	1,395
Net current period other comprehensive income (loss)		(35,271)	19,056	(11,004)
Reclassification of certain income tax effects	[2]		0
Ending balance		2,836,260	2,668,749	2,581,526
Total
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		(25,498)	(40,036)	(29,032)
Adjusted beginning balance			(25,839)
Cumulative effect adjustment of change in accounting policy, net of tax impact	[1]		(341)
Reclassification of certain income tax effects	[2]		(4,518)
Ending balance		(61,110)	(25,498)	(40,036)
Unrealized gains (losses) on securities carried at fair value, net of tax
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		(10,348)	(14,142)	(1,888)
Adjusted beginning balance			(10,692)
Cumulative effect adjustment of change in accounting policy, net of tax impact			(344)
Other comprehensive income (loss) before reclassifications		(26,903)	826	(12,170)
Amounts reclassified from accumulated other comprehensive income (loss)		(177)	4,802	(84)
Net current period other comprehensive income (loss)		(27,080)	5,628	(12,254)
Reclassification of certain income tax effects			(1,834)
Ending balance		(37,772)	(10,348)	(14,142)
Defined Benefit Pension Plans
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		(19,808)	(25,894)	(27,144)
Adjusted beginning balance			(19,808)
Cumulative effect adjustment of change in accounting policy, net of tax impact			0
Other comprehensive income (loss) before reclassifications		0	8,457	(229)
Amounts reclassified from accumulated other comprehensive income (loss)		(8,958)	1,139	1,479
Net current period other comprehensive income (loss)		(8,958)	9,596	1,250
Reclassification of certain income tax effects			(3,510)
Ending balance		(28,766)	(19,808)	(25,894)
Unrealized gains (losses) on cash flow hedges, net of tax
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		4,658	0	0
Adjusted beginning balance			4,661
Cumulative effect adjustment of change in accounting policy, net of tax impact			3
Other comprehensive income (loss) before reclassifications		2,245	2,771	0
Amounts reclassified from accumulated other comprehensive income (loss)		(1,478)	1,061	0
Net current period other comprehensive income (loss)		767	3,832	0
Reclassification of certain income tax effects			826
Ending balance		$ 5,428	$ 4,658	$ 0

[1] Refer to Note 1, Summary of Significant Accounting Policies, Note 4, Investment Securities, Note 7, Other Real Estate Owned and Repossessed Assets and Note 9, Loan Servicing Rights, for further details on the changes in accounting policy.

[2] The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, refer to Note 1 for further details on the adoption.