Commitments and Contingencies Lease Contractual obligation (Details)		3 Months Ended	6 Months Ended
	Mar. 01, 2019 USD ($) ft²	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Leases [Abstract]
Operating Lease Term	5 years
Finance lease right-of-use assets		$ 23,900,000	$ 23,900,000
Finance Lease, Right-of-Use Asset, Amortization		1,800,000	3,300,000
Operating Leases, Future Minimum Payments Due, Next Twelve Months		28,500,000	28,500,000	$ 47,400,000
Capital Leases, Future Minimum Payments Due, Next Twelve Months		3,700,000	3,700,000	6,600,000
Operating Leases, Future Minimum Payments, Due in Two Years		50,900,000	50,900,000	38,400,000
Capital Leases, Future Minimum Payments Due in Two Years		6,500,000	6,500,000	5,400,000
Operating Leases, Future Minimum Payments, Due in Three Years		37,800,000	37,800,000	27,200,000
Capital Leases, Future Minimum Payments Due in Three Years		4,900,000	4,900,000	3,800,000
Operating Leases, Future Minimum Payments, Due in Four Years		25,800,000	25,800,000	17,900,000
Capital Leases, Future Minimum Payments Due in Four Years		3,100,000	3,100,000	2,100,000
Operating Leases, Future Minimum Payments, Due in Five Years		19,700,000	19,700,000	12,700,000
Capital Leases, Future Minimum Payments Due in Five Years		1,200,000	1,200,000	900,000
Operating Leases, Future Minimum Payments, Due Thereafter		19,200,000	19,200,000	16,100,000
Capital Leases, Future Minimum Payments Due Thereafter		11,700,000	11,700,000	12,800,000
Operating Leases, Future Minimum Payments Due		181,900,000	181,900,000	159,700,000
Capital Leases, Future Minimum Payments Due		31,100,000	31,100,000	31,600,000
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(14,700,000)	(14,700,000)
Finance Lease, Liability, Undiscounted Excess Amount		1,100,000	1,100,000
Capital Leases, Future Minimum Payments, Interest Included in Payments				(2,100,000)
Operating Lease, Liability		167,200,000	167,200,000
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments		30,000,000.0	30,000,000.0	29,500,000
Finance Lease, Interest Expense		200,000	300,000
Operating Lease, Cost		14,900,000	29,300,000
Short-term Lease, Cost		1,200,000	2,300,000
Variable Lease, Cost		5,200,000	10,100,000
Lease, Cost		23,300,000	45,300,000
Operating lease right-of-use assets		166,200,000	166,200,000	0
Finance lease liability, current		6,600,000	6,600,000
Finance lease liability, non-current		23,400,000	23,400,000
Operating lease liability, current		49,600,000	49,600,000	0
Operating lease liability, non-current		$ 117,600,000	$ 117,600,000	$ 0
Weighted-average remaining lease term - finance leases		5 years 3 months 21 days	5 years 3 months 21 days
Weighted-average remaining lease term - operating leases		4 years 3 months	4 years 3 months
Weighted-average discount rate - finance leases		2.18%	2.18%
Weighted-average discount rate – operating leases		3.97%	3.97%
Area of Leased Office Building | ft²	192,000
Purchase Price of Property at End of Lease Term	$ 41,200,000
Percentage of Lease Balance as Final Payment End of Lease Term	87.00%
debt instrument, Covenant for debt not paid	$ 75,000,000
Operating cash flows from operating leases		$ 14,700,000	$ 27,400,000
Financing cash flows from finance leases		2,300,000	3,800,000
Right-of-use assets obtained in exchange for new finance lease liabilities		2,800,000	6,000,000.0
Right-of-use assets obtained in exchange for new operating lease liabilities		$ 5,000,000.0	$ 21,600,000