Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income taxes currently payable	$ 41,946	$ 38,732	$ 36,792
Deferred income taxes	8,412	23,251	9,832
Provision for income taxes	$ 50,358	$ 61,983	$ 46,624

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration