Accumulated Other Comprehensive Income (Loss) - Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pre-tax Amount
Balance	$ (159,423)	$ (145,472)	$ (84,722)
Other comprehensive income (loss)	(21,492)	(13,951)	(60,750)
Balance	(180,915)	(159,423)	(145,472)
Income Tax Benefit (Expense)
Balance	63,040	57,461	33,463
Other comprehensive income (loss)	5,748	5,579	23,998
Balance	48,720	63,040	57,461
Net of tax
Balance	2,532,551	2,476,485	2,736,941
Net of Tax	264,394	183,682	230,178
Other comprehensive loss	(15,744)	(8,372)	(36,752)
Balance	2,524,839	2,532,551	2,476,485
Early Adoption | ASU 2018-02
Income Tax Benefit (Expense)
Early adoption of ASU No. 2018-02	(20,068)
Net of tax
Other comprehensive loss	(20,068)
Accumulated other comprehensive loss
Net of tax
Balance	(96,383)	(88,011)	(51,259)
Other comprehensive loss	(15,744)	(8,372)	(36,752)
Balance	(132,195)	(96,383)	(88,011)
Accumulated other comprehensive loss | Early Adoption | ASU 2018-02
Net of tax
Other comprehensive loss	(20,068)
Pension and other benefits, net actuarial losses arising during the year
Pre-tax Amount
Unrealized net (losses) gains arising during the period	(2,835)	(1,104)	(12,666)
Reclassification of net losses (gains) to net income	7,315	8,625	7,629
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	763	436	5,004
Reclassification of net losses (gains) to net income	(1,970)	(3,407)	(3,012)
Net of tax
Unrealized net gains (losses) arising during the period	(2,072)	(668)	(7,662)
Reclassification of net losses (gains) to net income	5,345	5,218	4,617
Pension and other benefits:
Pre-tax Amount
Other comprehensive income (loss)	4,051	7,092	(5,547)
Income Tax Benefit (Expense)
Other comprehensive income (loss)	(1,091)	(2,801)	2,193
Net of tax
Balance	(25,946)	(30,237)	(26,883)
Other comprehensive loss	2,960	4,291	(3,354)
Balance	(28,379)	(25,946)	(30,237)
Pension and other benefits: | Early Adoption | ASU 2018-02
Net of tax
Other comprehensive loss	(5,393)
Pension and other benefits, prior service credit
Pre-tax Amount
Reclassification of net losses (gains) to net income	(429)	(429)	(429)
Income Tax Benefit (Expense)
Reclassification of net losses (gains) to net income	116	170	169
Net of tax
Reclassification of net losses (gains) to net income	(313)	(259)	(260)
Pension and other benefits, change due to the Reorganization Transactions
Pre-tax Amount
Reclassification of net losses (gains) to net income			(81)
Income Tax Benefit (Expense)
Reclassification of net losses (gains) to net income			32
Net of tax
Reclassification of net losses (gains) to net income			(49)
Investment securities:
Pre-tax Amount
Unrealized net (losses) gains arising during the period	(43,545)	(23,516)	(30,323)
Reclassification of net losses (gains) to net income			(27,277)
Other comprehensive income (loss)	(19,460)	(23,516)	(57,600)
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	11,686	9,357	11,974
Reclassification of net losses (gains) to net income			10,774
Other comprehensive income (loss)	5,201	9,357	22,748
Net of tax
Balance	(74,117)	(59,958)	(25,106)
Unrealized net gains (losses) arising during the period	(31,859)	(14,159)	(18,349)
Reclassification of net losses (gains) to net income			(16,503)
Other comprehensive loss	(14,259)	(14,159)	(34,852)
Balance	(103,816)	(74,117)	(59,958)
Investment securities: | Early Adoption | ASU 2018-02
Net of tax
Other comprehensive loss	(15,440)
Investment securities, OTTI losses on AFS debt securities, net
Pre-tax Amount
Reclassification of net losses (gains) to net income	24,085
Income Tax Benefit (Expense)
Reclassification of net losses (gains) to net income	6,485
Net of tax
Reclassification of net losses (gains) to net income	17,600
Cash flow derivative hedges:
Pre-tax Amount
Unrealized net (losses) gains arising during the period	1,475	2,473	2,397
Reclassification of net losses (gains) to net income	(7,558)
Other comprehensive income (loss)	(6,083)	2,473	2,397
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	(397)	(977)	(943)
Reclassification of net losses (gains) to net income	2,035
Other comprehensive income (loss)	1,638	(977)	(943)
Net of tax
Balance	3,680	2,184	730
Unrealized net gains (losses) arising during the period	1,078	1,496	1,454
Reclassification of net losses (gains) to net income	(5,523)
Other comprehensive loss	(4,445)	1,496	1,454
Balance		$ 3,680	$ 2,184
Cash flow derivative hedges: | Early Adoption | ASU 2018-02
Net of tax
Other comprehensive loss	$ 765