Summary of Significant Accounting Policies - Property, Equipment and Capitalized Software Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Corporate Headquarters [Member]
Property Plant And Equipment [Line Items]
List price of buildings	$ 3.0
Carrying value of buildings	1.2
Corporate Administrative Office Building [Member]
Property Plant And Equipment [Line Items]
List price of buildings	3.0
Carrying value of buildings	$ 1.8
Minimum [Member]
Property Plant And Equipment [Line Items]
Property, equipment and capitalized software, useful life	1 year
Minimum [Member] | Capitalized Software [Member]
Property Plant And Equipment [Line Items]
Property, equipment and capitalized software, useful life	2 years
Maximum
Property Plant And Equipment [Line Items]
Property, equipment and capitalized software, useful life	30 years
Maximum | Capitalized Software [Member]
Property Plant And Equipment [Line Items]
Property, equipment and capitalized software, useful life	5 years