Summary of Significant Accounting Policies - Carrying Amount and Fair Value of Financial Instruments (Details) - Term Loan - Level 3 - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans payable	$ 153,338	$ 152,838
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans payable	$ 162,052	$ 152,838

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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