Investments (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Average remaining maturities for short-term available for sale investments, in months	6 months
Average remaining maturities for long-term available for sale investments, in years	3 years
Realized gains on the sales of available-for-sale investments	$ 800	$ 1,900
Realized losses on the sales of available-for-sale investments	1,000	500
Available-for-sale investments, carrying value	1,397,439	1,602,904
Available-for-sale investments, fair value	1,394,816	1,602,370
Gross unrealized losses	3,493	2,116
Cost method investments	19,900	16,600
Cost method investments, gain recorded on cost method investments	8,700	2,900
Cost method investment, impairment charge included other income	$ 3,300	$ 8,300	$ 3,700