Pension and Other Postretirement Benefit Plans - Assets that are Carried at Fair Value, and the Method Used to Determine Fair Value (Details) - Retirement Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pooled Separate Accounts
Plan Investments	$ 25,505	$ 22,419	$ 22,702
Long Duration Bond Fund [Member]
Pooled Separate Accounts
Plan Investments	11,242	10,045
Long Corporate Bond Fund [Member]
Pooled Separate Accounts
Plan Investments	5,069	4,471
Prudential Short-term [Member]
Pooled Separate Accounts
Plan Investments	403	360
Investment Grade Bond Fund [Member]
Pooled Separate Accounts
Plan Investments	$ 8,791	$ 7,543