Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Previously recorded Alternative Minimum Tax		$ 3,500		$ 3,300
Decrease in deferred tax asset as a result of the Tax Cuts and Jobs Act of 2017						$ 54,600
Income tax provision (benefit)	$ (1,037)		$ (1)	$ (838)	$ 2