Income Taxes (Details) kr in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2016 DKK (kr)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 DKK (kr)	Mar. 31, 2017	Mar. 31, 2018 DKK (kr)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 DKK (kr)
Income Tax Examination [Line Items]
Effective income tax provision (as a percent)		30.50%	30.50%	31.30%
Statutory U.S. federal income tax (as a percent)		21.00%	21.00%	35.00%
Unrecognized tax benefits that would impact effective tax rate		$ 33.7				$ 31.7
Danish Tax Authority (SKAT) | Foreign Tax Authority
Income Tax Examination [Line Items]
Royalty rate (as a percent)		20.00%	20.00%
Cumulative total tax assessment		$ 274.6			kr 1,661.1	264.3	kr 1,638.4
Unrecognized tax benefits		142.2			861.0	137.9	855.0
Deferred tax assets		49.0				48.3
Valuation allowance		19.3				17.6
VAT taxes withheld by tax authority		59.1			357.5	54.2	336.5
Deposit paid to SKAT	kr 615.2	101.7
VAT refund applied to income tax liability		37.1	kr 224.6
Danish Tax Authority (SKAT) | Foreign Tax Authority | Tax Years 2001-2011
Income Tax Examination [Line Items]
Unrecognized tax benefits		138.2			836.0	134.9	836.0
Danish Tax Authority (SKAT) | Foreign Tax Authority | Tax Years After 2011
Income Tax Examination [Line Items]
Unrecognized tax benefits		$ 4.0			kr 24.0	$ 3.0	kr 18.0