Investment in Joint Venture Arrangements Investment in Joint Venture Arrangements Income Statement Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Revenue	$ 10,286	$ 5,995	$ 5,800
Costs and expenses	6,817	5,849	3,527
Income (loss)	3,469	146	2,273
Equity in Income (loss) from joint venture arrangements	$ 539	$ 477	$ 499