Cash, cash equivalents, short-term investments and restricted cash - Short Term Investments and Restricted Cash and Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and cash equivalents:
Cash	$ 70,467	$ 58,185
Cash equivalents	0	0
Cash and cash equivalents	70,467	58,185
Short-term investments	7,638	7,481
Cash and cash equivalents	70,467	58,185
Restricted cash	10,972	11,053
Total cash, cash equivalents and restricted cash shown in the consolidated statement of cash flows	$ 81,439	$ 69,238	$ 81,564	$ 86,585