Pension and Post-Retirement Benefits - Fair Value of Pension Plan Assets, by Asset Category (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	$ 110,431	$ 102,396
Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	1,385	2,449
Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,942	6,638
Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	19,183	11,689
Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	20,738	14,226
Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	8,416	6,819
Small-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets		522
Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,309	3,192
Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	37,664	43,745
U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	10,894	8,486
Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	2,496	3,578
Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	404	1,052
Level 1
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	106,146	95,317
Level 1 | Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 1 | Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,942	6,638
Level 1 | Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	19,183	11,689
Level 1 | Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	20,738	14,226
Level 1 | Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	8,416	6,819
Level 1 | Small-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets		522
Level 1 | Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,309	3,192
Level 1 | Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	37,664	43,745
Level 1 | U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	10,894	8,486
Level 1 | Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 1 | Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,285	7,079
Level 2 | Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	1,385	2,449
Level 2 | Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Small-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets		0
Level 2 | Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	2,496	3,578
Level 2 | Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	404	1,052
Level 3
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Small-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets		0
Level 3 | Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	$ 0	$ 0