Investment Securities (Details 4) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Realized gains (losses) on marketable investment securities
Realized gains from the sales of available-for-sale marketable investment securities		$ 19,100,000
Realized losses from the sales of marketable investment securities	0
Proceeds from sales of available-for-sale marketable investment securities	500,000	41,500,000
Fair value of marketable investment securities in a loss position
Less than 12 months	346,835,000		571,592,000
12 months or more	3,987,000
Total	350,822,000		571,592,000
Unrealized losses on marketable investment securities in a loss position
Less than 12 months	(306,000)		(825,000)
Total	$ (306,000)		$ (825,000)