Securities Available For Sale (Narrative) (Detail) (USD $)	12 Months Ended								27 Months Ended		39 Months Ended		12 Months Ended					12 Months Ended					39 Months Ended		12 Months Ended			15 Months Ended	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Auction Rate Securities [Member]		Dec. 31, 2011 Auction Rate Securities [Member]		Dec. 31, 2010 Auction Rate Securities [Member]	Dec. 31, 2011 Auction Rate Securities [Member]		Dec. 31, 2012 Auction Rate Securities [Member]		Dec. 31, 2012 Minimum [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Maximum [Member] Auction Rate Securities [Member]	Jun. 30, 2011 Asset Backed Securities Redeemed [Member]	Dec. 31, 2012 Asset-backed Securities [Member]	Dec. 31, 2011 Asset-backed Securities [Member]	Dec. 31, 2012 Collateralized Debt Obligations [Member] Auction Rate Securities [Member] Y		Dec. 31, 2011 Collateralized Debt Obligations [Member] Auction Rate Securities [Member]		Dec. 31, 2010 Collateralized Debt Obligations [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Collateralized Debt Obligations [Member] Auction Rate Securities [Member] Y		Dec. 31, 2012 Collateralized Debt Obligations [Member] Minimum [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Collateralized Debt Obligations [Member] Maximum [Member] Auction Rate Securities [Member]	Dec. 31, 2010 Collateralized Debt Obligations Sold [Member] Auction Rate Securities [Member]	Dec. 31, 2010 Collateralized Debt Obligations Sold [Member] Auction Rate Securities [Member]	Jun. 30, 2011 Asset Backed Securities Redeemed [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Asset-backed Securities [Member] Auction Rate Securities [Member]		Dec. 31, 2011 Asset-backed Securities [Member] Auction Rate Securities [Member]		Dec. 31, 2012 Asset-backed Securities [Member] Minimum [Member] Auction Rate Securities [Member] Y	Dec. 31, 2012 Asset-backed Securities [Member] Maximum [Member] Auction Rate Securities [Member] Y
Schedule of Available-for-sale Securities [Line Items]
Investment, debt security, default rate of underlying assets																		6.22%							8.00%	9.00%
Auction-rate securities yield rate													1.68%	2.37%
Interest earned on auction rate securities				$ 400,000		$ 400,000		$ 700,000
Cumulative credit and other losses recognized in earnings	0	574,000	1,164,000						3,300,000		3,300,000							0		600,000		1,200,000	3,300,000					4,600,000
Par value of securities held				17,900,000		17,900,000			17,900,000		17,900,000							5,000,000					5,000,000				11,200,000	11,200,000
Adjusted cost basis				14,600,000	[1]	14,600,000	[1]		14,600,000	[1]	14,600,000	[1]						1,700,000	[1]	1,700,000	[1]		1,700,000	[1]			6,600,000	6,600,000		12,900,000	[1]	12,900,000	[1]
Unrealized gains on structured finance security																		1,000,000		0			1,000,000
Proceeds from sale of structured finance auction rate securities																											7,000,000
Cumulative realized losses on auction rate securities																												4,200,000
Gain on sale of auction rate securities																											400,000
Redemption of student loan auction rate securities at par																													4,600,000
Cumulative unrealized losses on auction rates securities															500,000	600,000	600,000
Reversal of unrealized losses on redeemed student loan auction rate securities, tax impact																													200,000
Gross cumulative losses on auction rate securities																														$ 1,200,000		$ 1,000,000
Contractual maturities of securities, in years																		4					4											15	35

[1] Adjusted cost basis reflects adjustments for credit and other losses recognized in earnings on our structured finance security. Cumulative adjustments to the cost basis of securities held as of both December 31, 2012 and 2011 totaled $3.3 million. Par value of securities held as of both December 31, 2012 and 2011 totaled $17.9 million.