Investments Schedule of Equity Securities (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Securities [Abstract]
Equity Securities at Fair Value	$ 514,900,000	$ 514,900,000
Equity Securities at Fair Value			$ 526,000,000
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount	0	200,000
Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Cumulative Amount	0	0
Equity Securities without Readily Determinable Fair Value, Downward Price Adjustment, Cumulative Amount	0	0
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Cumulative Amount	$ 200,000	$ 200,000