Changes in Mortgage Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Mortgage Loans on Real Estate [Line Items]
Balance at beginning of year	$ 165,000	$ 165,000	$ 200,164
New mortgage loans and additional advances on existing loans	203,650		7,836
Mortgage loans on real estate including additions during year	368,650	165,000	208,000
Collection of principal			(43,000)
Deductions during year			(43,000)
Balance at end of year	$ 368,650	$ 165,000	$ 165,000