Commitments and Contingencies - Additional Information (Details) £ in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) $ / £	Jun. 30, 2019 GBP (£) $ / £
Commitments And Contingencies [Line Items]
Purchase Commitments	$ 18.5
Long-term purchase commitment, Amount	$ 83.7
Pension Plan, Defined Benefit
Commitments And Contingencies [Line Items]
Defined benefit plan, estimated future employer contributions in current fiscal year, description	We have a contributory defined benefit plan that covers certain employees in the United Kingdom.  As of June 30, 2019, the unfunded liability for this defined benefit plan was approximately $27.7 million.  We are obligated to make annual contributions, each year through December 2029, of approximately GBP 2 million (approximately $2.6  million based on a GBP: USD exchange rate of 1.3:1).  The trustees are required to review the funding position every three years, and the most recent review was carried out in April 2019.  We anticipate receiving the outcome of the April 2019 review during the third quarter of 2019. The outcome of future reviews can result in a change in the amount of the payment.
Defined benefit plan, expected future benefit payments in year one	$ 2.6	£ 2
Defined benefit plan, expected future benefit payments in year two	2.6	2
Defined benefit plan, expected future benefit payments in year three	2.6	2
Defined benefit plan, expected future benefit payments in year four	2.6	2
Defined benefit plan, expected future benefit payments in year five	2.6	2
Defined benefit plan, expected future benefit payments in eight fiscal years thereafter	$ 2.6	£ 2
GBP:USD exchange rate | $ / £	1.3	1.3
Unfunded liability of defined benefit plan	$ 27.7