Schedule of Condensed Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change In Accounting Principle
Total assets	$ 2,429,345	$ 2,188,639
Total liabilities	650,990	683,579
Common stock	23,488	22,948
Additional paid-in capital	1,347,762	1,293,130
Accumulated other comprehensive (loss) income	5,820	4,746
Retained earnings	401,285	184,236
Total shareholders' equity	1,778,355	1,505,060	1,122,188	664,579
Total liabilities and shareholders' equity	2,429,345	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)