Investments Contractual Maturities of Investments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost	$ 328,339
Due one year through five years, Cost	412,095
Due after ten years, Cost	11,400
Amortized Cost	751,834	715,702
Due in one year or less, Estimated Fair Value	328,437
Due one year through five years, Estimated Fair Value	412,437
Due after ten years, Estimated Fair Value	11,025
Total, Estimated Fair Value	$ 751,899