Restricted Cash - Reconciliation of Cash and Cash Equivalents, and Restricted Cash to the Total of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents		$ 19,292	$ 11,809	$ 8,207	$ 6,042
Restricted cash - current	[1]		11,191
Restricted cash - non-current		1,273	1,266	1,247	1,843
Total of cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows		$ 20,565	$ 24,266	$ 9,454	$ 7,885

[1] Restricted cash – current as of December 31, 2017 represents amount held in an escrow account for the acquisition of The Future Customer (TFC). See Note 10 – Business Combination.