Pension and Retirement Plans, Deferred Compensation Arrangement with Individual, Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Assets [Abstract]
Company's 401(K) contributions for the year	$ 6,977	$ 7,451	$ 7,182
SERP [Member]
Defined Benefit Plan Assets [Abstract]
Income expense due to change in the fair market value of Company stock held in the SERP	616	1,556	$ 575
Cost [Member]
Defined Benefit Plan Assets [Abstract]
Plan Assets	6,151	7,148
Cost [Member] | Company Stock [Member]
Defined Benefit Plan Assets [Abstract]
Plan Assets	1,714	1,886
Cost [Member] | Equity Securities [Member]
Defined Benefit Plan Assets [Abstract]
Plan Assets	4,437	5,262
Market [Member]
Defined Benefit Plan Assets [Abstract]
Plan Assets	6,645	6,641
Market [Member] | Company Stock [Member]
Defined Benefit Plan Assets [Abstract]
Plan Assets	2,018	1,658
Market [Member] | Equity Securities [Member]
Defined Benefit Plan Assets [Abstract]
Plan Assets	$ 4,627	$ 4,983