Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Additional Information (Details)

v2.4.1.9
Fair Value Measurements - Additional Information (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Carrying value of senior notes $ 900,000us-gaap_UnsecuredLongTermDebt $ 900,000us-gaap_UnsecuredLongTermDebt
Revolving bank credit facility 447,000us-gaap_LongTermLineOfCredit 290,000us-gaap_LongTermLineOfCredit
Fair Value, Inputs, Level 2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Revolving bank credit facility $ 447,000us-gaap_LongTermLineOfCredit
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
$ 290,000us-gaap_LongTermLineOfCredit
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member