Summary of Significant Accounting Policies - Short-Term Investments, Restricted Cash and Inventories (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Short-term Investments
Unrealized gains (losses) on available-for-sale securities	$ 0.0	$ 0.0
Restricted Cash
Maximum period until release for current restricted cash	1 year
Inventories
Inventory adjustment, usage period	12 months