Summary of Significant Accounting Policies - Adoption of ASU 2015-05 Intangibles – Goodwill and Other – Internal Use Software (Details) - ASU 2015-05 “Intangibles – Goodwill and Other – Internal Use Software - Expected $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Adoption of Accounting Standards Updates
Assets from acquired software	$ 6.4
Amortization expense	$ 6.1