Fair Value of Financial Instruments - Financial Assets and Liabilities (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Carrying Amount
Assets:
Cash equivalents	$ 0	$ 30
Liabilities:
Senior notes	800,000	800,000
Term loans, recorded in long-term debt and current maturities of long-term debt	591,153	474,058
Derivative liabilities, recorded in accrued expenses and deferred credits	4,068	1,161
Carrying Amount | Other current assets
Assets:
Derivative assets, recorded in other current assets	1,372	8,234
Carrying Amount | Other assets
Assets:
Derivative assets, recorded in other current assets	6
Total Fair Value
Assets:
Cash equivalents	0	30
Liabilities:
Senior notes	823,500	692,000
Term loans, recorded in long-term debt and current maturities of long-term debt	593,932	455,545
Derivative liabilities, recorded in accrued expenses and deferred credits	4,068	1,161
Total Fair Value | Other current assets
Assets:
Derivative assets, recorded in other current assets	1,372	8,234
Total Fair Value | Other assets
Assets:
Derivative assets, recorded in other current assets	6
Total Fair Value | Level 1
Assets:
Cash equivalents	0	0
Liabilities:
Senior notes	0	0
Term loans, recorded in long-term debt and current maturities of long-term debt	0	0
Derivative liabilities, recorded in accrued expenses and deferred credits	0	0
Total Fair Value | Level 1 | Other current assets
Assets:
Derivative assets, recorded in other current assets	0	0
Total Fair Value | Level 1 | Other assets
Assets:
Derivative assets, recorded in other current assets	0
Total Fair Value | Level 2
Assets:
Cash equivalents	0	30
Liabilities:
Senior notes	823,500	692,000
Term loans, recorded in long-term debt and current maturities of long-term debt	593,932	455,545
Derivative liabilities, recorded in accrued expenses and deferred credits	4,068	1,161
Total Fair Value | Level 2 | Other current assets
Assets:
Derivative assets, recorded in other current assets	1,372	8,234
Total Fair Value | Level 2 | Other assets
Assets:
Derivative assets, recorded in other current assets	6
Total Fair Value | Level 3
Assets:
Cash equivalents	0	0
Liabilities:
Senior notes	0	0
Term loans, recorded in long-term debt and current maturities of long-term debt	0	0
Derivative liabilities, recorded in accrued expenses and deferred credits	0	0
Total Fair Value | Level 3 | Other current assets
Assets:
Derivative assets, recorded in other current assets	0	0
Total Fair Value | Level 3 | Other assets
Assets:
Derivative assets, recorded in other current assets	0
Cash and short-term investments | Carrying Amount
Assets:
Pension plan assets	8,787	7,254
Cash and short-term investments | Total Fair Value
Assets:
Pension plan assets	8,787	7,254
Cash and short-term investments | Total Fair Value | Level 1
Assets:
Pension plan assets	0	0
Cash and short-term investments | Total Fair Value | Level 2
Assets:
Pension plan assets	8,787	7,254
Cash and short-term investments | Total Fair Value | Level 3
Assets:
Pension plan assets	0	0
U.S. Government and agency obligations | Carrying Amount
Assets:
Pension plan assets	25,206	24,622
U.S. Government and agency obligations | Total Fair Value
Assets:
Pension plan assets	25,206	24,622
U.S. Government and agency obligations | Total Fair Value | Level 1
Assets:
Pension plan assets	25,206	24,622
U.S. Government and agency obligations | Total Fair Value | Level 2
Assets:
Pension plan assets	0	0
U.S. Government and agency obligations | Total Fair Value | Level 3
Assets:
Pension plan assets	0	0
Corporate and foreign bonds | Carrying Amount
Assets:
Pension plan assets	104,430	90,490
Corporate and foreign bonds | Total Fair Value
Assets:
Pension plan assets	104,430	90,490
Corporate and foreign bonds | Total Fair Value | Level 1
Assets:
Pension plan assets	0	0
Corporate and foreign bonds | Total Fair Value | Level 2
Assets:
Pension plan assets	104,430	90,490
Corporate and foreign bonds | Total Fair Value | Level 3
Assets:
Pension plan assets	0	0
Equity securities | Carrying Amount
Assets:
Pension plan assets	28,249	22,378
Equity securities | Total Fair Value
Assets:
Pension plan assets	28,249	22,378
Equity securities | Total Fair Value | Level 1
Assets:
Pension plan assets	28,249	22,378
Equity securities | Total Fair Value | Level 2
Assets:
Pension plan assets	0	0
Equity securities | Total Fair Value | Level 3
Assets:
Pension plan assets	0	0
Mutual funds | Carrying Amount
Assets:
Pension plan assets	70,230	60,099
Mutual funds | Total Fair Value
Assets:
Pension plan assets	70,230	60,099
Mutual funds | Total Fair Value | Level 1
Assets:
Pension plan assets	0	0
Mutual funds | Total Fair Value | Level 2
Assets:
Pension plan assets	70,230	60,099
Mutual funds | Total Fair Value | Level 3
Assets:
Pension plan assets	0	0
Common and collective funds | Carrying Amount
Assets:
Pension plan assets	132,600	110,596
Common and collective funds | Total Fair Value
Assets:
Pension plan assets	132,600	110,596
Common and collective funds | Total Fair Value | Level 1
Assets:
Pension plan assets	0	0
Common and collective funds | Total Fair Value | Level 2
Assets:
Pension plan assets	0	0
Common and collective funds | Total Fair Value | Level 3
Assets:
Pension plan assets	0	0
Common and collective funds | Total Fair Value | Assets measured at NAV
Assets:
Pension plan assets	$ 132,600	$ 110,596