Investment Securities (Details 4) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Realized gains (losses) on marketable investment securities
Realized losses from the sales of marketable investment securities	$ 0	$ 0
Proceeds from sales of available-for-sale marketable investment securities	87,100,000	500,000
Fair value of marketable investment securities in a loss position
Less than 12 months	848,813,000		968,941,000
12 months or more	14,000,000
Total	862,813,000		968,941,000
Unrealized losses on marketable investment securities in a loss position
Less than 12 months	(2,875,000)		(4,929,000)
12 months or more	(3,000)
Total	$ (2,878,000)		$ (4,929,000)