Revision of 2011 and 2012 Financial Statements - Effect of Revisions on Affected Line Items on Consolidated Statement of Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Comprehensive Income Data:
Net income	$ (39,381)	$ 9,424	$ 20,204	$ (17,271)	$ (10,074)	$ 42,458	$ 45,941	$ 60,645	$ (27,024)	$ 138,970	$ 309,086
Comprehensive income									(15,948)	140,519	304,116
As Previously Reported [Member]
Statement of Comprehensive Income Data:
Net income										140,465	307,752
Comprehensive income										142,014	302,782
Revisions [Member]
Statement of Comprehensive Income Data:
Net income										(1,495)	1,334
Comprehensive income										$ (1,495)	$ 1,334