Short- and Long-Term Investments and Investments on Deposit for Licensure (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Amortized cost and fair value of available-for-sale debt securities by contractual maturity
Maturing within one year, amortized cost	$ 551,658
Maturing within one year, fair value	552,129
Maturing between one year and five years, amortized cost	739,375
Maturing between one year and five years, fair value	741,922
Maturing between five years and ten years, amortized cost	192,856
Maturing between five years and ten years, fair value	205,905
Maturing in greater than ten years, amortized cost	97,845
Maturing in greater than ten years, fair value	99,737
Total, amortized cost	1,581,734
Total, fair value	$ 1,599,693

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