Debt - Summary of Debt and Capital Lease Obligations (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total Debt	$ 1,508,679	$ 1,154,420
Less amounts due within one year	(511)	(599)
Total long-term debt	1,508,168	1,153,821
$1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Total Debt	527,000	509,500
$400 Million Term Loan Facility [Member]
Debt Instrument [Line Items]
Total Debt	399,000
5% Senior Notes [Member]
Debt Instrument [Line Items]
Total Debt	350,000	350,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Total Debt	511	958
3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Total Debt	$ 232,168	$ 293,962