Retirement Plans - Pension Plan Assets (Details) - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Benefit Plans
Fair value of plan assets	$ 13,915	$ 169,484	$ 32,844
Measurement of fair value on a recurring basis
Employee Benefit Plans
Fair value of plan assets		170,215
Market value		0
Measurement of fair value on a recurring basis | Cash
Employee Benefit Plans
Fair value of plan assets	12,515	3,579
Measurement of fair value on a recurring basis | U.S. Treasury and government sponsored agency bonds and notes
Employee Benefit Plans
Fair value of plan assets		86,952
Measurement of fair value on a recurring basis | Mutual funds
Employee Benefit Plans
Fair value of plan assets		69,845
Measurement of fair value on a recurring basis | Corporate bonds
Employee Benefit Plans
Fair value of plan assets		6,718
Measurement of fair value on a recurring basis | Mortgage-backed securities
Employee Benefit Plans
Fair value of plan assets		2,346
Measurement of fair value on a recurring basis | Other assets
Employee Benefit Plans
Fair value of plan assets		775
Measurement of fair value on a recurring basis | Level 1
Employee Benefit Plans
Fair value of plan assets		74,199
Measurement of fair value on a recurring basis | Level 1 | Cash
Employee Benefit Plans
Fair value of plan assets	12,515	3,579
Measurement of fair value on a recurring basis | Level 1 | U.S. Treasury and government sponsored agency bonds and notes
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 1 | Mutual funds
Employee Benefit Plans
Fair value of plan assets		69,845
Measurement of fair value on a recurring basis | Level 1 | Corporate bonds
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 1 | Mortgage-backed securities
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 1 | Other assets
Employee Benefit Plans
Fair value of plan assets		775
Measurement of fair value on a recurring basis | Level 2
Employee Benefit Plans
Fair value of plan assets		96,016
Measurement of fair value on a recurring basis | Level 2 | Cash
Employee Benefit Plans
Fair value of plan assets	0	0
Measurement of fair value on a recurring basis | Level 2 | U.S. Treasury and government sponsored agency bonds and notes
Employee Benefit Plans
Fair value of plan assets		86,952
Measurement of fair value on a recurring basis | Level 2 | Mutual funds
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 2 | Corporate bonds
Employee Benefit Plans
Fair value of plan assets		6,718
Measurement of fair value on a recurring basis | Level 2 | Mortgage-backed securities
Employee Benefit Plans
Fair value of plan assets		2,346
Measurement of fair value on a recurring basis | Level 2 | Other assets
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 3
Employee Benefit Plans
Fair value of plan assets	0	0
Measurement of fair value on a recurring basis | Level 3 | Cash
Employee Benefit Plans
Fair value of plan assets	$ 0	0
Measurement of fair value on a recurring basis | Level 3 | U.S. Treasury and government sponsored agency bonds and notes
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 3 | Mutual funds
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 3 | Corporate bonds
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 3 | Mortgage-backed securities
Employee Benefit Plans
Fair value of plan assets		0
Measurement of fair value on a recurring basis | Level 3 | Other assets
Employee Benefit Plans
Fair value of plan assets		$ 0