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		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents		$ 6,304	$ 11,694	$ 6,322	$ 11,809
Restricted cash - current	[1]				11,191
Restricted cash - non-current			1,292	1,279	1,266
Total of cash, cash equivalents, and restricted cash shown in the consolidated statements of cash flows		$ 6,304	$ 12,986	$ 7,601	$ 24,266

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