Variable Interest Entities - Schedule of Carrying Value of Assets and Liabilities Eliminated from Financial Statement (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Feb. 28, 2013	Dec. 31, 2012	Mar. 31, 2012
Receivables [Abstract]
Other assets		$ 6,614
Total assets	783,286	6,614	675,204	662,850
Other current liabilities	52,185	3,060	106,796	60,641
Other liabilities		43,054
Total	$ 674,601	$ 46,114	$ 549,439	$ 571,349