Retirement Agreements and Other Postretirement Benefit Plan Changes in Amounts Related to Accumulated Other Comprehensive Income, Pre-tax (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of year	$ 165,437	$ 173,812
Unrecognized prior service cost	0	0	$ (4,390)
Amortization of loss, net	(8,612)	(8,941)	(3,514)
Actuarial (gain) loss	(69,634)	566	63,566
Balance at end of year	$ 87,191	$ 165,437	$ 173,812