Summary of Significant Accounting Policies - Operating expense (Details) - General and administrative - ASU 2016-02 $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	$ 1,296
Under Topic 840
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	1,164
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	$ 132