Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, amount recognized	$ 51.7
Maximum | Pro Forma | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability		$ 30.0
Minimum | Pro Forma | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability		$ 28.0