Employee Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2014
Investment
Assets contributed to 401(k) Plan					$ 7,900
401(k) Plan distribution period (in years)			3 years
Compensation expense for assets allocated to participants			$ 1,100	$ 1,200
Realized gain (loss)		$ 7,700	(1,086)	10,861
Restricted | Maximum
Investment
Realized gain (loss)	$ (100)	$ 100	$ (100)	$ 100