Fair Values Of Assets And Liabilities (Narrative) (Detail) (USD $)																					3 Months Ended			3 Months Ended												3 Months Ended			3 Months Ended				3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Jun. 30, 2012	Mar. 31, 2012		Mar. 31, 2013 Municipal Bonds [Member]	Dec. 31, 2012 Municipal Bonds [Member]	Mar. 31, 2012 Municipal Bonds [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Municipal Bonds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Municipal Bonds [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Municipal Bonds [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Equity Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Equity Securities [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Equity Securities [Member]	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Other Real Estate Owned [Member] Minimum [Member]	Mar. 31, 2013 Other Real Estate Owned [Member] Maximum [Member]	Mar. 31, 2013 Level 3 [Member]	Mar. 31, 2013 Level 3 [Member] Equity Securities [Member]	Mar. 31, 2013 Level 3 [Member] Equity Securities [Member] Minimum [Member]	Mar. 31, 2013 Level 3 [Member] Equity Securities [Member] Maximum [Member]	Mar. 31, 2013 Level 3 [Member] Mortgage Servicing Rights [Member]	Mar. 31, 2013 Level 3 [Member] Mortgage Servicing Rights [Member] Minimum [Member]	Mar. 31, 2013 Level 3 [Member] Mortgage Servicing Rights [Member] Maximum [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Mar. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds [Member]	Dec. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds [Member]	Mar. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Equity Securities [Member]	Dec. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Equity Securities [Member]	Mar. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Equity Securities [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Equity Securities [Member] Minimum [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Equity Securities [Member] Maximum [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Mortgage Servicing Rights [Member]	Mar. 31, 2013 Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Level 3 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value [Member]	Dec. 31, 2012 Fair Value [Member]	Mar. 31, 2012 Fair Value [Member]	Mar. 31, 2013 Valued Using Discounted Cash Flow Model [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 1,870,831,000		$ 1,796,076,000			$ 1,869,344,000		$ 110,259,000	$ 110,471,000	$ 69,915,000				$ 110,259,000	$ 110,471,000	$ 69,915,000	$ 52,057,000	$ 49,699,000	$ 38,496,000														$ 32,324,000	$ 30,770,000	$ 25,535,000	$ 24,470,000	$ 22,169,000	$ 21,224,000
Fair Value Inputs, Discount Rate																					0.00%	100.00%		1.39%	1.20%	1.52%	10.19%	10.00%	13.50%										1.20%	1.52%
Mortgage servicing rights											7,344,000	6,750,000	7,201,000																		6,750,000	7,201,000									7,344,000
Fair Value Inputs, Prepayment Rate																											18.32%	16.00%	22.00%
Remaining contractual principal balance outstanding, mortgage loans held-for-sale																																												366,800,000	379,500,000	329,900,000
Mortgage loans held-for-sale											370,570,000	385,033,000	339,600,000																	0	0	0
Mortgages held for sale, past due 90 days and accruing	0		0			0
Total impaired loans	203,554,000	[1]	204,545,000	[1]		251,963,000	[1]																																								82,400,000
Impaired Loans Fair Value Disclosure																				121,200,000																						121,197,000
Other real estate owned																																										56,177,000	56,177,000
Weighted Average of Inputs																																				1.39%							4.44%
Secured borrowings-owed to securitization investors	$ 0		$ 0		$ 360,800,000	$ 428,000,000																	$ 0

[1] Impaired loans are considered by the Company to be non-accrual loans, restructured loans or loans with principal and/or interest at risk, even if the loan is current with all payments of principal and interest.