Debt - Summary of Debt (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Principal amount	$ 1,616,371
Debt	1,618,981	1,421,681
2011 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	6.875%	6.875%
Debt	450,000	450,000
Revolving credit facility [Member]
Debt Instrument [Line Items]
Interest rate	Variable	Variable
Debt		105,000
2006 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Interest rate	Various	Various
Debt	125,000	125,000
2012 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	6.375%	6.375%
Principal amount	350,000	350,000
Unamortized premium	2,610	2,873
Debt	352,610	352,873
2013 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	5.75%	5.75%
Debt	252,620	274,860
2014 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	5.50%
Debt	300,000
Term Loan [Member]
Debt Instrument [Line Items]
Interest rate	Various	Various
Debt	$ 138,751	$ 113,948