Investments (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Certificates of deposits	$ 5,000	$ 5,500
Certificates of deposit interest rate, lower range	0.85%
Certificates of deposit interest rate, upper range	1.10%
Investments held to maturity	$ 11,342	$ 14,083
Minimum
Schedule of Investments [Line Items]
Certificates of deposit maturity dates	1 month
Investments maturity dates	2 months
Maximum
Schedule of Investments [Line Items]
Certificates of deposit maturity dates	12 months
Investments maturity dates	10 months