Leases (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Leases [Abstract]
Operating lease cost	$ 4.1
Operating Lease Cost [Abstract]
Operating lease cost	4.0
Short-term lease cost	0.1
Operating cash flows information [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	4.0
Non-cash activity [Abstract]
Right-of-use assets obtained in the exchange for operating lease liabilities	$ 0.2
Weighted Average Remaining Lease Term and Discount Rates [Abstract]
Weighted-average remaining operating lease term	7 years 10 months 13 days
Weighted-average operating leases discount rate	5.00%
Outstanding Lease Assets and Liabilities [Abstract]
Right-of-use asset	$ 47.4
Lease liability - current	12.3
Lease liability - non-current	46.1
Future Minimum Lease Payments [Abstract]
For the remainder of 2019	11.5
2020	12.3
2021	9.0
2022	7.2
2023	5.9
Thereafter	25.3
Total future minimum lease payments	71.2
Less imputed interest	(13.0)
Total	$ 58.2
Minimum Lease Payments under Non-cancellable Operating Leases [Abstract]
2019		$ 17.3
2020		13.0
2021		9.5
2022		8.2
2023		7.0
Thereafter		24.8
Total		79.8
Rent Expense [Abstract]
Rent expense		$ 19.5	$ 19.3
Minimum [Member]
Operating Leases [Abstract]
Remaining lease terms	1 year
Maximum [Member]
Operating Leases [Abstract]
Remaining lease terms	50 years