Debt - Summary of Debt and Capital Lease Obligations (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total Debt	$ 1,154,046	$ 1,154,420
Less amounts due within one year	(604)	(599)
Total long-term debt	1,153,442	1,153,821
$1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Total Debt	506,000	509,500
5% Senior Notes [Member]
Debt Instrument [Line Items]
Total Debt	350,000	350,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Total Debt	810	958
3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Total Debt	$ 297,236	$ 293,962