Consolidated Statements of Changes In Equity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated other comprehensive (loss) income:
Beginning Balance	$ 51,009		$ 85,264	$ 60,329
Other comprehensive loss				(27,293)
Ending balance	56,182	33,036	56,182	33,036
Retained earnings:
Beginning Balance			1,744,684	1,514,866
Net income	82,739	50,089	166,726	164,351
Cash dividends declared				(35,715)
Ending Balance	1,292,993	1,643,502	1,292,993	1,643,502
As Previously Reported
Accumulated other comprehensive (loss) income:
Beginning Balance				(222,922)
Other comprehensive loss				(8,717)
Ending balance		(231,639)		(231,639)
Retained earnings:
Beginning Balance				1,798,117
Net income		37,732		145,775
Cash dividends declared				(35,715)
Ending Balance		1,908,177		1,908,177
Effect of Accounting Change
Accumulated other comprehensive (loss) income:
Beginning Balance				283,251
Other comprehensive loss				(18,576)
Ending balance		264,675		264,675
Retained earnings:
Beginning Balance				(283,251)
Net income		12,357		18,576
Ending Balance		$ (264,675)		$ (264,675)