Debt - Summary of Debt Net of Discounts (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long term debt	$ 1,086,973	$ 1,025,160
Revolving credit facility
Debt Instrument [Line Items]
Interest rate	Variable	Variable
Principal amount	45,000	125,000
2006 Senior Unsecured Notes
Debt Instrument [Line Items]
Interest rate	Various	Various
Principal amount	125,000	125,000
2011 Senior Unsecured Notes
Debt Instrument [Line Items]
Unsecured senior notes, interest rate	6.875%	6.875%
Principal amount	450,000	450,000
2012 Senior Unsecured Notes
Debt Instrument [Line Items]
Unsecured senior notes, interest rate	6.375%	6.375%
Principal amount	350,000	200,000
Unamortized premium	2,960
Debt instrument, net	352,960	200,000
Exchangeable senior notes
Debt Instrument [Line Items]
Unsecured senior notes, interest rate		9.25%	[1]
Principal amount		11,000	[1]
Unamortized discount		(37)
Debt instrument, net		10,963
Term loans
Debt Instrument [Line Items]
Interest rate	Various	Various
Debt instrument, net	$ 114,013	$ 114,197

[1] The exchangeable senior notes were paid in full on April 1, 2013.