Long-Term Cash Incentive Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments
Performance condition period		3 years
Long Term Incentive Plan 2019
Deferred Compensation Arrangement with Individual, Share-based Payments
Accrued compensation expense			$ 1.5
Long Term Incentive Plan 2016
Deferred Compensation Arrangement with Individual, Share-based Payments
Accrued compensation expense		$ 1.2		$ 1.3
Payment of plan including employer cost	$ 4.2