Significant Accounting Policies - Recently Issued Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 3,800
Operating lease, liability	$ 4,200
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, weighted average discount rate, percent	5.60%
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, weighted average discount rate, percent	9.10%
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment for accounting changes related to leases and tax reorganizations (Note 2)	$ 400	$ (389)	$ 0	$ 124,476