Commitments and Contingencies - Other Commitments and Legal Matters (Details) $ in Millions	Oct. 18, 2018 USD ($) item	Jul. 18, 2016 item	Jul. 12, 2016 item	Dec. 31, 2015 complaint
Legal matters
Number of putative securities class action complaints filed against the Company \| complaint				2
Number of additional purported shareholder derivative actions filed		2	2
Regatta Against Company
Legal matters
Alleged number of frauds	2
Regatta Against Executive Vice President
Legal matters
Alleged number of frauds	1
Minimum \| Regatta Against Company
Legal matters
Claim for general and compensatory damages \| $	$ 1.5
Minimum \| Regatta Against Executive Vice President
Legal matters
Claim for general and compensatory damages \| $	$ 1.5