Leases - Narrative (Details) $ in Thousands		1 Months Ended
	Mar. 06, 2019 a item	Jan. 31, 2017 USD ($) a	Mar. 31, 2019 USD ($) ft²	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Leases
Operating lease right-of-use assets, net			$ 1,378
Operating lease liability			$ 1,672
Accounting Standards Update 2016-02
Leases
Operating lease right-of-use assets, net		$ 2,300
Operating lease liability		$ 2,300
Cumulative effect adjustment from adoption of ASU 2016-01					$ 213
Accounting Standards Update 2016-02 | Adjustments
Leases
Operating lease right-of-use assets, net				$ 1,600
Operating lease liability				1,900
Deferred rent				(100)
Cumulative effect adjustment from adoption of ASU 2016-01				$ 200
Office space lease
Leases
Area of property leased | ft²			25,600
Operating lease right-of-use assets, net			$ 606
Land leases
Leases
Operating lease right-of-use assets, net			$ 772
City Of Texas City and State Of Texas (Galveston Bay) | Surface leases
Leases
Area of land leased/to be leased | a		994
Term of lease agreement		36 months
Existence of option to extend		true
Option to extend term		12 months
BND | Land leases
Leases
Area of land leased/to be leased | a	984
Term of lease agreement	30 years
Maximum period for automatic extension for Outside Effective Date	6 months
Number of renewal term | item	2
Option to extend term	10 years
Option to extend term, lease not yet commenced	true