Lease Obligations - Summary of lease-related assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets
Operating lease right-of-use assets	$ 22,968	$ 0
Finance lease right-of-use assets	1,781
Total right-of-use lease assets	24,749
Current
Operating lease obligations	6,068	0
Finance lease obligations	1,144	1,119
Total current obligations	7,212
Non-current
Operating lease obligations	17,084	0
Finance lease obligations	633	$ 1,514
Total non-current obligations	17,717
Total lease obligations	$ 24,929