Investments Additional Information (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Money market funds	$ 34,200,000	$ 34,200,000
Debt securities	625,055,000	625,055,000
Preferred stock	3,487,000	3,487,000
Realized losses from the sale of available-for-sale securities	400,000	800,000
Sales of investments	5,600,000	8,239,000	0
Maturities of investments	35,000,000	60,000,000	0
Gross unrealized losses	1,941,000	1,941,000		2,213,000
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities	524,814,000	524,814,000
Number of securities with net unrealized losses	0	0
Gross unrealized losses	0	0		0
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities	100,241,000	100,241,000
Held-to-maturity securities, continuous unrealized loss position, twelve months or longer, fair value	11,100,000	11,100,000
Held-to-maturity securities, continuous unrealized loss position, twelve months or longer, accumulated loss	800,000	800,000
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, fair value	89,100,000	89,100,000		22,000,000
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss	1,100,000	1,100,000		2,200,000
Gross unrealized losses	$ 1,941,000	$ 1,941,000		$ 2,213,000
Required percent of investment account held in cash or cash equivalents | Minimum
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations		50.00%
Other aggregated investments | Securities of any one issuer (excluding the U.S. Government) | Minimum
Schedule of Available-for-sale Securities [Line Items]
Investments, portfolio allocations requiring additional consent		10.00%
Other aggregated investments | Securities of any one issuer (excluding the U.S. Government) | Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations		15.00%
Investments, portfolio allocations requiring additional consent		15.00%
Investor | Fairholme Capital Management, L.L.C.
Schedule of Available-for-sale Securities [Line Items]
Common stock ownership percentage	27.10%	27.10%