Notes Payable (Detail Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Notes Payable [Abstract]
Interest rate of senior notes	6.30%
Senior note, face amount			$ 300.0
Senior note, unamortized discount	1.5
Senior note, effective interest rate	6.37%
Borrowing capacity under line of credit facility	825.0	600.0
Borrowing rate under revolving loan facility	125.00%
Contractual interest rate on borrowing under facility	1.40%
Commitment fees basis points for revolving loan facility	15.00%
Remaining borrowing capacity under Revolving Loan Facility as reduced by outstanding letters of credit	294.1
Leverage ratio on restrictive financial covenants	35
Letter of credit facility outstanding amount	90.0
Line of credit facility expiration date	Apr. 30, 2019
Outstanding letters of credit reduced our borrowing capacity	5.9
Subsidiary letter of credit facility outstanding amount	6.3
Senior Notes Payable Fair Value	352.7	350.1
Annual Dividend Restrictions In Excess Of The Greater Of Amount	$ 150.0
Annual Dividend Restrictions In Excess Of The Greater Of Percentage	33.00%