Reconciliation of Total Segment Assets to Total Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting, Asset Reconciling Item [Line Items]
Total segment assets	$ 3,226,103	$ 2,944,744	$ 2,136,168
Other assets	67,440	34,343
Total assets	$ 3,293,543	$ 2,979,087