Investments (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Certificates of deposits	$ 3,100	$ 5,500
Certificates of deposit interest rate, lower range	0.55%
Certificates of deposit interest rate, upper range	0.90%
Investments held to maturity	$ 7,139	$ 14,083
Minimum [Member]
Schedule of Investments [Line Items]
Certificates of deposit maturity dates	1 month
Investments maturity dates	1 month
Maximum [Member]
Schedule of Investments [Line Items]
Certificates of deposit maturity dates	4 months
Investments maturity dates	3 months