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, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents		$ 5,689	$ 11,694	$ 19,292	$ 11,809
Restricted cash - current	[1]				11,191
Restricted cash - non-current			1,292	1,273	1,266
Total of cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows		$ 5,689	$ 12,986	$ 20,565	$ 24,266

[1] Restricted cash – current at the beginning of 2018 represents amount held in an escrow account for a business acquisition.