Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Operating Loss Carryforwards	$ 28,600	$ 28,600
Deferred tax assets, state net operating loss carryforward	15,400	15,400
Increase in tax expense attributable to revaluation of deferred tax assets	25,800
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		564	$ 450	$ 357
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance of unrecognized tax benefits		29,004	28,879	5,975
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions		(1,054)	(44)	(327)
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions		1,433	169	23,231
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities		(1,128)	0	0
Ending balance of unrecognized tax benefits	28,255	28,255	29,004	28,879
Current tax expense
Federal		95,151	87,992	84,946
State		21,523	6,116	7,493
Total current tax expense		116,674	94,108	92,439
Deferred Income Tax Expense (Benefit)
Federal		(10,944)	115,392	23,144
State		(2,433)	10,446	10,002
Total deferred tax expense		(13,377)	125,838	33,146
Total income tax expense		$ 103,297	219,946	125,585
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory rate		21.00%
Income taxes at federal statutory rates		$ 105,758	190,294	122,874
Nontaxable income on loans, leases and investments, net of nondeductible expenses		(1,796)	(2,525)	(2,901)
Nondeductible FDIC insurance expense		2,348	0	0
State and local income taxes, including change in valuation allowance, net of federal income tax benefit		15,081	10,765	11,372
Effect of federal rate change		(15,736)		0
Tax credits net of amortization		(2,891)	(4,840)	(4,138)
Other, net		533	490	(1,622)
Total income tax expense		103,297	219,946	$ 125,585
Deferred Tax Assets, Net [Abstract]
Allowance for loan and lease losses	53,391	53,391	50,853
Pension liability	0	0	704
Executive separation from service agreements	7,927	7,927	8,548
Federal net operating loss carryforward	6,862	6,862	2,685
Net unrealized loss included in comprehensive income	32,663	32,663	10,849
Employee compensation	11,145	11,145	4,192
Deferred Tax Assets, FDIC-Assisted Transaction Timing Differences	7,622	7,622	0
Deferred Tax Assets, Other reserves	5,574	5,574	5,570
Other	9,555	9,555	5,924
Deferred tax asset	134,739	134,739	89,325
Deferred Tax Liabilities, accelerated depreciation	4,987	4,987	7,562
Lease financing activities	12,674	12,674	9,131
Net deferred loan fees and costs	10,651	10,651	8,708
Intangible assets	11,713	11,713	12,252
Deferred Tax Liability, Security, loan and debt valuations	4,557	4,557	7,018
FDIC-assisted transactions timing differences	0	0	1,113
Pension liability	6,287	6,287	0
Other	1,722	1,722	4,565
Deferred tax liability	52,591	52,591	50,349
Net deferred tax assets	$ 82,148	$ 82,148	$ 38,976