Investment Securities (Detail) - Cumulative credit-related losses recognized in earnings (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cumulative credit related losses recognized in earnings at beginning of period	$ 8,894	$ 8,391
Cumulative credit related losses recognized in earnings at end of period	9,162	8,460
Additions
Credit loss for which previous OTTI was recognized	268	69
Collateralized Debt Obligations [Member]
Cumulative credit related losses recognized in earnings at beginning of period	5,823	5,782
Cumulative credit related losses recognized in earnings at end of period	5,823	5,823
Additions
Credit loss for which previous OTTI was recognized	0	41
Collateralized Mortgage Obligations [Member]
Cumulative credit related losses recognized in earnings at beginning of period	1,971	1,509
Cumulative credit related losses recognized in earnings at end of period	2,239	1,537
Additions
Credit loss for which previous OTTI was recognized	268	28
Equity Securities, Other [Member]
Cumulative credit related losses recognized in earnings at beginning of period	1,100	1,100
Cumulative credit related losses recognized in earnings at end of period	1,100	1,100
Additions
Credit loss for which previous OTTI was recognized	$ 0	$ 0