Incentive Plans - Schedule of Issuance of RSUs and Charges to Retained Earnings (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
Jun. 30, 2014	Jun. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of RSUs issued	203,537	135,044
Charges to retained earnings, net of estimated forfeitures	$ 9,387	$ 4,173

Charge To Retained Earnings Pertaining To Issuance Of Restricted Stock Units In Connection With Participation Rights

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration