Leases - Operating lease (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Leases
Operating lease right-of-use assets, net	$ 1,608		$ 1,608
Total current lease liabilities	1,784		1,784
Non-current lease liabilities	273		273
Operating lease liability	2,057		2,057
Operating lease expense
Total operating lease expense	267		503
Short-term lease expense	25		40
Land option expense	159		319
Total land option and lease expense	451	$ 250	862	$ 500
Office space lease
Leases
Operating lease right-of-use assets, net	976		976
Total current lease liabilities	977		977
Non-current lease liabilities	273		273
Operating lease expense
Total operating lease expense	146		262
Land leases
Leases
Operating lease right-of-use assets, net	632		632
Total current lease liabilities	807		807
Operating lease expense
Total operating lease expense	$ 121		$ 241