Notes Payable and Long-Term Debt - Revolving Credit Facilities (Details) (USD $)	12 Months Ended
	Dec. 31, 2013
Prudential facility
Line of Credit Facility [Line Items]
Revolving credit maximum borrowing capacity	$ 300,000,000
Line of credit term of facility	3 years
Total remaining capacity available for borrowing	2,500,000
A and B Senior Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit maximum borrowing capacity	350,000,000
Line of credit term of facility	5 years
Uncommitted increase option	100,000,000
Sub limit for the issuance of standby and commercial letters of credit	100,000,000
Sub limit for swing line loans	80,000,000
Outstanding letters of credit	11,400,000
Total remaining capacity available for borrowing	243,600,000
Line of credit facility outstanding amount	95,000,000
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Unused borrowing capacity	246,100,000
Subsidiary, One
Line of Credit Facility [Line Items]
Line of credit facility outstanding amount	17,100,000
Subsidiary, One | Line of Credit
Line of Credit Facility [Line Items]
Face amount of debt	40,000,000
Subsidiary, Two
Line of Credit Facility [Line Items]
Line of credit facility outstanding amount	4,000,000
Subsidiary, Two | Line of Credit
Line of Credit Facility [Line Items]
Face amount of debt	$ 4,000,000