Leases - Operating lease (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases
Operating lease right-of-use assets, net	$ 1,378
Total current lease liabilities	1,320
Non-current lease liabilities	352
Operating lease liability	1,672
Operating lease expense
Total operating lease expense	236
Short-term lease expense	32
Land option expense	160
Total land option and lease expense	428	$ 250
Amortization of right-of-use assets	184
Office space lease
Leases
Operating lease right-of-use assets, net	606
Total current lease liabilities	510
Non-current lease liabilities	327
Operating lease expense
Total operating lease expense	116
Land leases
Leases
Operating lease right-of-use assets, net	772
Total current lease liabilities	810
Non-current lease liabilities	25
Operating lease expense
Total operating lease expense	$ 120