Income Taxes - Income Tax (Benefit) (Details)	3 Months Ended									12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Currently payable tax:
Federal										$ 7,631,000	$ 9,187,000	$ 12,948,000
State										4,689,000	5,416,000	4,653,000
Total currently payable										$ 12,320,000	14,603,000	17,601,000
Tax Cuts and Jobs Act of 2017 effect on re-measurement of net deferred tax assets									$ 7,103,000			7,103,000
Number of items for which the Company was unable to make a reasonable estimate for the effects of the tax law change | item										0
Deferred tax (benefit):
Federal										$ 2,200,000	(1,133,000)	1,193,000
Due to enactment of Tax Reform									$ 7,103,000			7,103,000
State										1,331,000	(146,000)	574,000
Total deferred tax										3,531,000	(1,279,000)	8,870,000
Income tax expense	$ 2,088,000	$ 4,633,000	$ 4,623,000	$ 4,507,000	$ 5,138,000	$ 4,979,000	$ (31,000)	$ 3,238,000		$ 15,851,000	$ 13,324,000	$ 26,471,000