Income Tax - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Currently Payable:
Federal									$ 23,938	$ 23,633	$ 22,001
State									422	1,842	0
Deferred:
Federal									4,726	6,723	9,969
Tax Cuts and Jobs Act - Rate Reform Impact									0	0	5,120
State									239	(3,199)	434
Income Tax Expense	$ 8,298	$ 6,337	$ 7,749	$ 6,941	$ 5,949	$ 8,478	$ 7,961	$ 6,611	$ 29,325	$ 28,999	$ 37,524