Summary of Significant Accounting Policies - Operating expense (Details) - General and administrative - ASU 2016-02 $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	$ 648
Under Topic 840
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	582
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	$ 66