Schedule of Condensed Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Change In Accounting Principle
Total assets	$ 2,463,291	$ 2,188,639
Total liabilities	678,048	683,579
Common stock	23,456	22,948
Additional paid-in capital	1,337,616	1,293,130
Accumulated other comprehensive (loss) income	6,343	4,746
Retained earnings	417,828	184,236
Total shareholders' equity	1,785,243	1,505,060
Total liabilities and shareholders' equity	2,463,291	2,188,639
Originally Reported
Change In Accounting Principle
Total assets		2,188,639
Total liabilities		683,579
Common stock		22,948
Additional paid-in capital		1,293,130
Accumulated other comprehensive (loss) income		(129,875)
Retained earnings		318,857
Total shareholders' equity		1,505,060
Total liabilities and shareholders' equity		2,188,639
Effect Of Accounting Change
Change In Accounting Principle
Accumulated other comprehensive (loss) income		134,621
Retained earnings		$ (134,621)