Employee Benefit Plans - Fair Value of Pension Plan Assets (Details) - Pension Plans - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,725,543	$ 1,941,330	$ 1,787,075
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,603,707	1,826,737
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121,836	114,593	$ 102,884
U.S. common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	315,741	443,405
U.S. common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	315,741	443,405
U.S. common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	352,040	458,111
Foreign common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	352,040	458,111
Foreign common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79,155	85,117
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79,155	85,117
Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	856,771	840,104
Common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	856,771	840,104
Common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity and hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121,836	114,593
Private equity and hedge funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity and hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity and hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 121,836	$ 114,593