Pension and Other Retirement Plans - Pension Plan Assets by Asset Category (Details) - Pension Plans - USD ($) $ in Thousands		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		$ 1,505,074		$ 1,660,001		$ 1,545,862
Total pension plan assets measured at fair value		1,091,504		1,274,569
Pension plan assets measured at NAV as a practical expedient (2)		387,922	[1]	360,382	[2]
Insurance contracts		25,648		25,050
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value		523,262		704,141
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value		568,242		570,428
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value		0		0
Registered investment companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		523,262		704,141
Registered investment companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		523,262		704,141
Registered investment companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Registered investment companies | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Common/collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		17,219		12,607
Common/collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Common/collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		17,219		12,607
Common/collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
U.S. government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		214,902		250,792
U.S. government securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
U.S. government securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		214,902		250,792
U.S. government securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		314,768		294,362
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		314,768		294,362
Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Mortgage-backed and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		20,841		31,188
Mortgage-backed and asset-backed securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Mortgage-backed and asset-backed securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		20,841		31,188
Mortgage-backed and asset-backed securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Other alternative investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		(15,247)	[3]	(35,330)	[4]
Other alternative investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0	[3]	0	[4]
Other alternative investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		(15,247)	[3]	(35,330)	[4]
Other alternative investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0	[3]	0	[4]
Pooled separate account
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		15,759		16,809
Pooled separate account | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Pooled separate account | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		15,759		16,809
Pooled separate account | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0		0
Pending net purchases
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	[4]	$ (58,000)		$ (89,000)

[1] (2)Certain common/collective trusts, the international equity limited liability company, real estate, private equity and venture capital limited partnerships that are measured at fair value using the NAV per share practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the total value of plan assets.

[2] (2)Certain common/collective trusts, the international equity limited company, real estate, private equity and venture capital limited partnerships that are measured at fair value using the NAV per share practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the total value of plan assets.

[3] Other includes pending net security purchases of $58 million.

[4] Other includes pending net security purchases of $89 million.