Investments - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012 Securities	Jun. 25, 2011	Jun. 30, 2012 Securities	Jun. 25, 2011	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Total realized gains on sales of AFS securities	$ 7,228,000	$ 13,476,000	$ 9,777,000	$ 22,736,000
Total realized losses on sales of AFS securities	3,064,000	949,000	5,375,000	2,176,000
Total, Unrealized Losses	$ 18,964,000		$ 18,964,000		$ 19,357,000
Number of AFS securities issues contributing to the total unrealized loss	353		353