Consolidated Statements of Changes In Equity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated other comprehensive (loss) income:
Beginning Balance	$ 85,264	$ 60,329
Other comprehensive income		28,722
Ending balance	51,009	89,051
Retained earnings:
Beginning Balance	1,744,684	1,514,866
Net income	83,987	114,262
Cash dividends declared		(17,824)
Ending Balance	1,744,100	1,611,304
As Previously Reported
Accumulated other comprehensive (loss) income:
Beginning Balance		(222,922)
Other comprehensive income		34,941
Ending balance		(187,981)
Retained earnings:
Beginning Balance		1,798,117
Net income		108,043
Cash dividends declared		(17,824)
Ending Balance		1,888,336
Effect of Accounting Change
Accumulated other comprehensive (loss) income:
Beginning Balance		283,251
Other comprehensive income		(6,219)
Ending balance		277,032
Retained earnings:
Beginning Balance		(283,251)
Net income		6,219
Ending Balance		$ (277,032)