Accumulated Other Comprehensive Loss, Net of Tax (Parenthetical) (Detail) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized losses on temporarily impaired investments, tax benefits	$ (8,492,000)	$ (7,278,000)
Unrealized gains on investments, taxes	18,343,000	32,684,000
Unrealized gains (losses) on derivatives, taxes (benefits)	(62,210,000)	(3,403,000)
Recognition of actuarial net loss from pension and other postretirement plans, tax benefits	$ (81,798,000)	$ (70,388,000)