Fair Value Measurements (Details 2) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Total
Interest in a limited partnership	$ 600,000	$ 600,000	$ 1,400,000
Stocks not carried at fair value	700,000	700,000
Fair Value Measurements Using Level 1
Assets
Investment securities	284,000	255,000
Fair Value Measurements Using Level 2
Assets
Investment securities	609,599,000	639,148,000
Fair Value Measurements Using Level 2 | Cross currency interest rate derivatives
Assets
Derivative Assets	14,049,000	26,699,000
Fair Value Measurements Using Level 3
Assets
Investment securities	29,807,000	29,767,000
Recurring basis | Fair Value Measurements Using Level 1
Assets
Cash and cash equivalents in mutual funds	1,113,743,000	630,227,000
Investment securities	284,000	255,000
Restricted cash in mutual funds	150,448,000	93,781,000
Total
Total	1,264,475,000	724,263,000
Recurring basis | Fair Value Measurements Using Level 1 | Common stocks
Assets
Investment securities	284,000	255,000
Recurring basis | Fair Value Measurements Using Level 2
Assets
Investment securities	609,599,000	639,148,000
Total
Total	623,648,000	665,847,000
Recurring basis | Fair Value Measurements Using Level 2 | Cross currency interest rate derivatives
Assets
Derivative Assets	14,049,000	26,699,000
Recurring basis | Fair Value Measurements Using Level 2 | Investment securities:
Assets
Investment securities	609,599,000	639,148,000
Recurring basis | Fair Value Measurements Using Level 2 | U.S. government and government sponsored entities
Assets
Investment securities	38,839,000	36,442,000
Recurring basis | Fair Value Measurements Using Level 2 | Obligations of states, municipalities, and political subdivisions
Assets
Investment securities	129,533,000	140,224,000
Recurring basis | Fair Value Measurements Using Level 2 | Corporate debt
Assets
Investment securities	251,502,000	274,272,000
Recurring basis | Fair Value Measurements Using Level 2 | RMBS
Assets
Investment securities	168,490,000	172,135,000
Recurring basis | Fair Value Measurements Using Level 2 | CMBS
Assets
Investment securities	15,209,000	12,899,000
Recurring basis | Fair Value Measurements Using Level 2 | CDO/ABS
Assets
Investment securities	6,026,000	3,176,000
Recurring basis | Fair Value Measurements Using Level 3
Assets
Investment securities	28,456,000	28,416,000
Total
Total	28,456,000	28,416,000
Recurring basis | Fair Value Measurements Using Level 3 | Investment securities:
Assets
Investment securities	27,116,000	27,036,000
Recurring basis | Fair Value Measurements Using Level 3 | Corporate debt
Assets
Investment securities	13,877,000	13,417,000
Recurring basis | Fair Value Measurements Using Level 3 | RMBS
Assets
Investment securities	65,000	74,000
Recurring basis | Fair Value Measurements Using Level 3 | CMBS
Assets
Investment securities	2,000	153,000
Recurring basis | Fair Value Measurements Using Level 3 | CDO/ABS
Assets
Investment securities	13,172,000	13,392,000
Recurring basis | Fair Value Measurements Using Level 3 | Other long-term investments
Assets
Investment securities	1,340,000	1,380,000
Recurring basis | Total Carried At Fair Value
Assets
Cash and cash equivalents in mutual funds	1,113,743,000	630,227,000
Investment securities	638,339,000	667,819,000
Restricted cash in mutual funds	150,448,000	93,781,000
Total
Total	1,916,579,000	1,418,526,000
Recurring basis | Total Carried At Fair Value | Out of period adjustment
Assets
Cash and cash equivalents in mutual funds		565,300,000
Recurring basis | Total Carried At Fair Value | Cross currency interest rate derivatives
Assets
Derivative Assets	14,049,000	26,699,000
Recurring basis | Total Carried At Fair Value | Investment securities:
Assets
Investment securities	636,715,000	666,184,000
Recurring basis | Total Carried At Fair Value | U.S. government and government sponsored entities
Assets
Investment securities	38,839,000	36,442,000
Recurring basis | Total Carried At Fair Value | Obligations of states, municipalities, and political subdivisions
Assets
Investment securities	129,533,000	140,224,000
Recurring basis | Total Carried At Fair Value | Corporate debt
Assets
Investment securities	265,379,000	287,689,000
Recurring basis | Total Carried At Fair Value | RMBS
Assets
Investment securities	168,555,000	172,209,000
Recurring basis | Total Carried At Fair Value | CMBS
Assets
Investment securities	15,211,000	13,052,000
Recurring basis | Total Carried At Fair Value | CDO/ABS
Assets
Investment securities	19,198,000	16,568,000
Recurring basis | Total Carried At Fair Value | Other long-term investments
Assets
Investment securities	1,340,000	1,380,000
Recurring basis | Total Carried At Fair Value | Common stocks
Assets
Investment securities	$ 284,000	$ 255,000