Investment And Other Gains Investment And Other Gains (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Marketable Securities, Realized Gain (Loss)	$ 0	$ 0	$ 10,038	$ 0
Proceeds from sales of marketable securities					$ 0	$ 18,182	$ 18,182
2017 Sales Transaction [Member]
Proceeds from sales of marketable securities			$ 11,718
Marketable securities								$ 11,745
Available-for-sale Securities, Amortized Cost Basis								$ 1,680
2016 Sales Transaction [Member]
Proceeds from sales of marketable securities							$ 6,464