Investments (Details 7) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 133,558,000	$ 292,486,000
Less Than 20 Percent [Member]
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	54,951,000	131,155,000
Percentage Of Total Gross Unrealized Losses	41.20%	44.80%
More Than Or Equal To 20 Percent For Less Than Six Months [Member]
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	734,000	51,503,000
Percentage Of Total Gross Unrealized Losses	0.50%	17.60%
More Than Or Equal To 20 Percent For Six Months Or Greater [Member]
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 77,873,000	$ 109,828,000
Percentage Of Total Gross Unrealized Losses	58.30%	37.60%