Employee Benefit Plans - Pension Plan Assets Measured at Fair Value (Details) - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets measured at fair values
Fair value of assets	$ 19,435	$ 17,500	$ 15,927
Cash
Assets measured at fair values
Fair value of assets	3,021	4,128
Equities
Assets measured at fair values
Fair value of assets	11,576	9,008
Mutual funds
Assets measured at fair values
Fair value of assets	4,838	4,364
Level 1
Assets measured at fair values
Fair value of assets	19,435	17,500
Level 1 | Cash
Assets measured at fair values
Fair value of assets	3,021	4,128
Level 1 | Equities
Assets measured at fair values
Fair value of assets	11,576	9,008
Level 1 | Mutual funds
Assets measured at fair values
Fair value of assets	$ 4,838	$ 4,364