Derivative Instruments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
6.9 percent senior notes due June 2013
Notional amounts
Interest rate stated percentage	6.90%
Designated hedge
Notional amounts
Change in net unrealized gain (loss) related to cash flow hedging instruments, net of taxes	$ 1,700,000	$ 1,200,000	$ 1,200,000
Income tax benefit associated with the gain resulting from settlements	653,000	462,000	462,000
Mortgage interest rate lock commitments ("IRLCs")
Notional amounts
Average number of days of interest rate commitment before closing	180 days
Interest rate, low end range	3.30%	3.30%
Interest rate, high end range	4.50%	4.50%
Notional amount	137,741,000	114,583,000
Forward-delivery contracts
Notional amounts
Notional amount	$ 68,000,000	$ 56,500,000