Commitments and Contingencies (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013 score	Dec. 31, 2012 score	Dec. 31, 2011 score	Dec. 31, 2010 score	Dec. 31, 2009 score	Dec. 31, 2008 score
Commitments and Contingencies
Mortgage loan types originated (as a percent)	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%
Average FICO credit score	731	731	726	723	717	711
Average combined loan-to-value ratio (as a percent)	90.30%	90.10%	90.30%	90.80%	91.40%	90.10%
Mortgage interest rate lock commitments ("IRLCs")
Commitments and Contingencies
Average number of days of interest rate commitment before closing	180 days
Notional amount	$ 411,800,000	$ 137,700,000
Development bonds
Commitments and Contingencies
Guarantee obligations estimated exposure pertaining to land development and improvements	127,300,000	108,400,000
Performance-related cash deposits and letters of credit
Commitments and Contingencies
Guarantee obligations estimated exposure pertaining to land development and improvements	63,100,000	52,000,000
Prime
Commitments and Contingencies
Mortgage loan types originated (as a percent)	54.50%	48.60%	42.20%	34.90%	32.90%	51.80%
Government (FHA/VA/USDA)
Commitments and Contingencies
Mortgage loan types originated (as a percent)	45.50%	51.40%	57.80%	65.10%	67.10%	48.20%
Lot option purchase contracts
Commitments and Contingencies
Cash deposits and/or letters of credit	73,300,000	53,100,000
Aggregate purchase price	934,700,000	589,600,000
Purchase commitments, specific performance	$ 2,800,000	$ 492,000