Restatement and Revision of Previously Issued Unaudited Financial Statements - Effect of Revisions on Affected Line Items on Condensed Consolidated Statement of Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Condensed Consolidated Statement of Comprehensive Income Data:
Net income	$ 20,204	$ 45,941	$ 2,932	$ 32,384	$ 106,586
Comprehensive income	20,252	46,110	3,075		106,918
As Previously Reported [Member]
Condensed Consolidated Statement of Comprehensive Income Data:
Net income	20,859	46,002	51,989		107,073
Comprehensive income	20,907	46,171	52,132		107,405
Revisions [Member]
Condensed Consolidated Statement of Comprehensive Income Data:
Net income		(61)			(487)
Comprehensive income		$ (61)			$ (487)