Investments (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Certificates of deposits	$ 12,700,000	$ 5,200,000
Certificates of deposit interest rate, lower range	0.10%
Certificates of deposit interest rate, upper range	0.90%
Investments held to maturity	$ 29,288,000	$ 10,873,000
Minimum [Member]
Schedule of Investments [Line Items]
Certificates of deposit maturity dates	2 months
Investments maturity dates	1 month
Maximum [Member]
Schedule of Investments [Line Items]
Certificates of deposit maturity dates	18 months
Investments maturity dates	18 months