Available-for-Sale Securities Summary of Available-for-Sale Securities by Contractual Maturity (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Less than 1 Year, Amortized Cost	$ 5,960,662
Greater than 1 Year but Less than 5 Years, Amortized Cost	773,969
Greater than 5 Years but Less than 10 Years, Amortized Cost	2,449
Greater than 10 Years, Amortized Cost	4,806
Total Amortized Cost	6,741,886
Less than 1 Year, Fair Value	5,960,893
Greater than 1 Year but Less than 5 Years, Fair Value	775,051
Greater than 5 Years but Less than 10 Years, Fair Value	2,458
Greater than 10 Years, Fair Value	4,806
Total	$ 6,743,208	$ 1,948,748