Fair Value Measurements - Schedule of Liabilities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Dec. 31, 2011
Liabilities:
Letters of Credit			$ 11,569
Long-term obligations	1,671,114	[1]	1,862,091	[2],[3]	1,468,543
Derivative financial instruments			1,880	[4],[5]
Assets:
Derivative financial instruments	347	[6]
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) [Member]
Liabilities:
Letters of Credit
Long-term obligations		[1]		[2],[3]
Derivative financial instruments				[4],[5]
Assets:
Derivative financial instruments		[6]
Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Letters of Credit			11,569
Long-term obligations	1,401,487	[1]	1,445,774	[2],[3]
Derivative financial instruments			1,880	[4],[5]
Assets:
Derivative financial instruments	347	[6]
Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Letters of Credit
Long-term obligations	269,627	[1]	416,317	[2],[3]
Derivative financial instruments				[4],[5]
Assets:
Derivative financial instruments		[6]

[1] Reflected at carrying value in the unaudited condensed consolidated balance sheet as current maturities on long-term debt of $14,050 and long-term debt of $1,629,489 as of September 30, 2013.

[2] Reflected at carrying value in the consolidated balance sheet as current maturities on long-term debt of $21,330 and long-term debt of $1,802,644. As of December 31, 2011, the carrying value and fair value of long-term obligations, including the current portion, was $1,417,887 and $1,468,543, respectively.

[3] Reflected at carrying value in the unaudited condensed consolidated balance sheet as current maturities on long-term debt of $21,330 and long-term debt of $1,802,644 as of December 31, 2012.

[4] Reflected at fair value in the consolidated balance sheet as other liabilities of $1,880.

[5] Reflected at fair value in the unaudited condensed consolidated balance sheet as other liabilities of $1,880 at December 31, 2012.

[6] Reflected at fair value in the unaudited condensed consolidated balance sheet as other assets of $347. There were no transfers between Levels 1, 2 or 3 during the three or nine months ended September 30, 2013.