Cash, cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and cash equivalents	$ 148,716	$ 133,407
Short-term and long-term restricted cash	6,877	7,473
Total cash, cash equivalents and long-term restricted cash	155,593	140,880	$ 120,688	$ 77,655
Letter of credit related to workers' compensation insurance	800	800
Letter of credit associated with bank guarantee one		700
Letter of credit associated with bank guarantee two	100
Deposit related to customs activity	100	100
Revolving credit facility
Restricted cash which relates to support of outstanding letters of credit	6,900	7,500
Revolving credit facility | Beverly Property Owner LLC
Letter of credit associated with security deposit for leaseback transaction	$ 5,900	$ 5,900