Condensed Consolidating Financial Information - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 Restatement Adjustment [Member] Subsidiaries Guarantor	Dec. 31, 2011 Restatement Adjustment [Member] Subsidiaries Guarantor	Dec. 31, 2012 Restatement Adjustment [Member] Subsidiaries Non Guarantor	Dec. 31, 2011 Restatement Adjustment [Member] Subsidiaries Non Guarantor	Dec. 31, 2012 Restatement Adjustment [Member] Eliminations	Dec. 31, 2011 Restatement Adjustment [Member] Eliminations
Total Assets	$ 2,563,150	$ 2,178,886	$ 1,010,400	$ 888,900	$ 390,900	$ 5,500	$ (1,401,300)	$ (894,400)
Total liabilities	$ 1,204,581	$ 1,129,072	$ 1,010,400	$ 888,900	$ 390,900	$ 5,500	$ (1,401,300)	$ (894,400)