Significant Accounting Policies - Summary of Cash After Implementing ASU 2016-18 (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018		Jun. 30, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 76,068	$ 71,064	[1]
Restricted cash	203	203	[1]
ASU 2016-18
Significant Accounting Policies [Line Items]
Cash and cash equivalents	76,068	71,064		$ 169,998	$ 98,426
Restricted cash	203	203		203	203
Cash, cash equivalents and restricted cash	$ 76,271	$ 71,267		$ 170,201	$ 98,629

[1] The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.