Other Long-Term Liabilities- New Jersey tax benefits (Details) - USD ($) $ in Thousands	1 Months Ended				12 Months Ended
	Nov. 30, 2015	Dec. 31, 2014	Jan. 31, 2014	Jan. 31, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment and other income					$ 4,214	$ 4,386	$ 2,344
New Jersey tax benefits
Amount of tax benefit	$ 9,800	$ 1,900	$ 1,100	$ 800
Proceeds from sale of tax credits	$ 9,200	$ 1,800	$ 1,000	$ 800
Base of operations requirement (in years)					5 years
Investment and other income					$ 2,700	$ 2,800	$ 1,000