Retirement Benefits - Summary of Basis Used to Measure Defined Benefit Plans Assets at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	$ 117,112	$ 112,505
U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	3,759	16,402
U.S. Small / Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	770	7,966
International, Equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	7,532	16,844
U.S. Intermediate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	581	13,568
U.S. Long Term
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	75,096
U.S. Short Duration
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		13,362
U.S. High Yield
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	1,098	9,529
International, Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	8,604	13,311
Other Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	15,555	16,059
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	1,944	2,613
Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	2,173	2,851
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	9,522	77,078
Level 1 | U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	3,759	16,402
Level 1 | U.S. Small / Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	7,051
Level 1 | International, Equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	4,445	13,205
Level 1 | U.S. Intermediate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	13,483
Level 1 | U.S. Long Term
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0
Level 1 | U.S. Short Duration
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		13,362
Level 1 | U.S. High Yield
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	8,462
Level 1 | International, Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	244	3,767
Level 1 | Other Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	1,074	1,346
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	92,035	19,368
Level 2 | U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 2 | U.S. Small / Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	770	915
Level 2 | International, Equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	3,087	3,639
Level 2 | U.S. Intermediate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	581	85
Level 2 | U.S. Long Term
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	75,096
Level 2 | U.S. Short Duration
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		0
Level 2 | U.S. High Yield
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	1,098	1,067
Level 2 | International, Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	8,360	9,544
Level 2 | Other Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	870	1,267
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	2,173	2,851
Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	15,555	16,059
Level 3 | U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | U.S. Small / Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | International, Equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | U.S. Intermediate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | U.S. Long Term
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0
Level 3 | U.S. Short Duration
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		0
Level 3 | U.S. High Yield
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | International, Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | Other Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	15,555	16,059
Level 3 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0	0
Level 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	$ 0	$ 0