Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Expected income taxes	$ 46,270	$ 77,214	$ 138,608	$ 214,997
Increase (reduction) in income taxes resulting from:
Low income housing investments	(2,779)	(4,367)	(9,428)	(13,665)
Share-based awards	(2,601)	(5,075)	(6,855)	(14,513)
Other	740	(508)	907	(3,429)
Income tax expense (benefit) from continuing operations	$ 41,630	$ 67,264	$ 123,232	$ 183,390
Expected income taxes	21.00%	35.00%	21.00%	35.00%
Increase (reduction) in income taxes resulting from:
Low income housing investments	(1.30%)	(2.00%)	(1.40%)	(2.20%)
Share-based awards	(1.20%)	(2.30%)	(1.00%)	(2.40%)
Other	0.40%	(0.20%)	0.10%	(0.50%)
Income tax expense (benefit) from continuing operations	18.90%	30.50%	18.70%	29.90%
Tax benefit as a result of remeasuring deferred tax assets and liabilities					$ 877,000

Effective Income Tax Rate Reconciliation, Excess Tax Benefit from Share-based Compensation, Percent

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The effective income tax rate reduction resulting from credits associated with low-income housing interests.

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Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act of 2017, Amount

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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