Debt - Summary of Debt and Capital Lease Obligations (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total Debt	$ 1,280,122	$ 1,154,420
Less amounts due within one year	(609)	(599)
Total long-term debt	1,279,513	1,153,821
$1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Total Debt	300,000	509,500
$400 Million Term Loan Facility [Member]
Debt Instrument [Line Items]
Total Debt	400,000
5% Senior Notes [Member]
Debt Instrument [Line Items]
Total Debt	350,000	350,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Total Debt	661	958
3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Total Debt	$ 229,461	$ 293,962