Commitments and Contingencies - Employment Contracts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Commitments [Line Items]
Severance costs		$ 1,783,000
Payments for Severance	$ (308,000)	(4,215,000)
Remaining severance liability	$ 63,000	371,000	$ 2,803,000
Selling and Marketing Expense
Other Commitments [Line Items]
Severance costs		500,000
Technology And Development
Other Commitments [Line Items]
Severance costs		1,300,000
Employment Contracts
Other Commitments [Line Items]
Period of severance obligations (up to)	12 months
Remaining severance liability	$ 0	200,000
Employment Contracts | Former CEO
Other Commitments [Line Items]
Bonus			100,000
Severance costs			500,000
Annual fee			100,000
Remaining severance liability	100,000	200,000
Employment Contracts | Former CEO | General and Administrative Expenses
Other Commitments [Line Items]
Severance costs			900,000
Employment Contracts | Former Executive-Level Employees
Other Commitments [Line Items]
Severance costs			2,500,000
Remaining severance liability	$ 0	$ 0
Employment Contracts | Former Executive-Level Employees | General and Administrative Expenses
Other Commitments [Line Items]
Severance costs			1,700,000
Employment Contracts | Former Executive-Level Employees | Selling and Marketing Expense
Other Commitments [Line Items]
Severance costs			400,000
Employment Contracts | Former Executive-Level Employees | Technology And Development
Other Commitments [Line Items]
Severance costs			$ 400,000