Components of Carrying Value of Residential Available for Sale Securities in Unrealized Loss Position (Detail) (Residential, USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Residential
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Consecutive Months Amortized Cost	$ 299,244	$ 22,803
Less Than 12 Consecutive Months Gross Unrealized Losses	(11,837)	(293)
Less Than 12 Consecutive Months Fair Value	287,407	22,510
12 Consecutive Months or Longer Amortized Cost	13,974	26,729
12 Consecutive Months or Longer Gross Unrealized Losses	(1,696)	(2,072)
12 Consecutive Months or Longer Fair Value	$ 12,278	$ 24,657