Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income taxes currently payable	$ 5,638	$ 11,946	$ 31,335	$ 30,467
Deferred income taxes	5,264	2,732	7,316	4,962
Provision for income taxes	$ 10,902	$ 14,678	$ 38,651	$ 35,429

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