Summary of Significant Accounting Policies - Newly-Adopted Accounting Pronouncements (Details) - USD ($) $ in Millions		12 Months Ended
Jan. 01, 2017	Dec. 31, 2017
Newly-Adopted Accounting Pronouncements
Increase in deferred tax and valuation allowance		$ 17.7
Adjustments for New Accounting Principle, Early Adoption \| Accounting Standards Update
Newly-Adopted Accounting Pronouncements
Increase in deferred tax and valuation allowance	$ 17.7

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