Summary of Significant Accounting Policies, Derivative Instruments, Foreign Exchange Contracts (Details) ¥ in Millions, $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2017 AUD ($)	Dec. 31, 2016 CAD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 JPY (¥)	Dec. 31, 2016 AUD ($)
Derivative [Line Items]
Expiration date of contract	Dec. 20, 2018
Foreign Exchange Contract [Member] | Canada, Dollars
Derivative [Line Items]
Foreign exchange contract outstanding				$ 0.5
Foreign Exchange Contract [Member] | Japan, Yen
Derivative [Line Items]
Foreign exchange contract outstanding | ¥		¥ 162.5				¥ 281.4
Foreign Exchange Contract [Member] | Euro [Member]
Derivative [Line Items]
Foreign exchange contract outstanding | €	€ 24,000.0				€ 100,000
Foreign Exchange Contract [Member] | Australian Dollars [Member]
Derivative [Line Items]
Foreign exchange contract outstanding			$ 0.2				$ 0.6