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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other investments		$ 5,300	$ 3,100
Reclassification of accumulated other comprehensive income due to statutory tax changes	$ 700
Minimum [Member]
Useful life		2 years
Maximum [Member]
Useful life		40 years
Employee Stock Option [Member]
Number of anti-dilutive securities			5,000	50,000