Employee Benefit Plans - Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Weighted average allocation of plan assets (as a percent)	100.00%	100.00%	100.00%
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 75,875	$ 62,952	$ 64,886
Minimum
Defined Benefit Plan Disclosure [Line Items]
Investment objective period to earn long-term expected rate of return	15 years
Maximum
Defined Benefit Plan Disclosure [Line Items]
Investment objective period to earn long-term expected rate of return	20 years
Level 1
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 837	129
Level 2
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	75,038	62,823
Cash.
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	837	129
Cash. | Level 1
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 837	$ 129
US and international equities
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Weighted average allocation of plan assets (as a percent)	29.90%	27.10%	45.00%
U.S.
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 13,121	$ 10,161
U.S. | Level 2
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	13,121	10,161
International
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	8,747	6,773
International | Level 2
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 8,747	$ 6,773
UK government and corporate bonds
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Weighted average allocation of plan assets (as a percent)	12.50%	12.70%	20.00%
Corporate bonds / UK Gilts
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 9,446	$ 7,987
Corporate bonds / UK Gilts | Level 2
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 9,446	$ 7,987
Diversified growth fund
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Weighted average allocation of plan assets (as a percent)	41.30%	38.90%	35.00%
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 31,345	$ 24,488
Diversified growth fund | Level 2
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 31,345	$ 24,488
Liability Driven Investments [Member]
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Weighted average allocation of plan assets (as a percent)	16.30%	21.30%
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 12,379	$ 13,414
Liability Driven Investments [Member] | Level 2
Defined Benefit Plan Pension Assets Fair Value By Category [Abstract]
Fair value of plan assets	$ 12,379	$ 13,414