Summary of Significant Accounting Policies - Long-Lived and Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment charges on long-lived assets	$ 0	$ 0
Impairment charges on definite lived intangible assets	$ 0	$ 0	$ 0
Discontinued Operations, Held-for-sale | Pike
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment charge on assets held for sale			$ 5,000,000