Investment Securities (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 US Government Agencies Debt Securities [Member]	Dec. 31, 2011 US Government Agencies Debt Securities [Member]	Sep. 30, 2011 US Government Agencies Debt Securities [Member]	Sep. 30, 2012 US States and Political Subdivisions Debt Securities [Member]	Dec. 31, 2011 US States and Political Subdivisions Debt Securities [Member]	Sep. 30, 2011 US States and Political Subdivisions Debt Securities [Member]	Sep. 30, 2012 Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Dec. 31, 2011 Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2011 Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2012 Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2012 Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]	Dec. 31, 2011 Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2011 Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2012 Non-agency [Member]	Dec. 31, 2011 Non-agency [Member]	Sep. 30, 2011 Non-agency [Member]	Sep. 30, 2012 Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Dec. 31, 2011 Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2012 Corporate Debt Securities [Member]	Dec. 31, 2011 Corporate Debt Securities [Member]	Sep. 30, 2011 Corporate Debt Securities [Member]	Sep. 30, 2012 Total debt securities [Member]	Dec. 31, 2011 Total debt securities [Member]	Sep. 30, 2011 Total debt securities [Member]	Sep. 30, 2012 Marketable equity securities [Member]	Dec. 31, 2011 Marketable equity securities [Member]	Sep. 30, 2011 Marketable equity securities [Member]	Sep. 30, 2012 Corporate Debt Securities [Member]	Sep. 30, 2012 US Government Debt Securities [Member]	Sep. 30, 2012 Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2012 Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]	Sep. 30, 2012 US States and Political Subdivisions Debt Securities [Member]	Dec. 31, 2011 US States and Political Subdivisions Debt Securities [Member]	Sep. 30, 2011 US States and Political Subdivisions Debt Securities [Member]	Sep. 30, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2011 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2010 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	$ 29,735,000	$ 179,133,000	$ 190,813,000	$ 182,781,000
Securities available for sale
Available-for-sale Securities, Amortized Cost	2,827,822,000	3,111,627,000	2,827,822,000	3,111,627,000	3,270,899,000	35,109,000	122,711,000	203,148,000	241,436,000	334,916,000	298,140,000	1,216,671,000	1,407,345,000	1,419,808,000	15,434,000	1,188,072,000	1,115,832,000	1,080,627,000	12,000	43,225,000	44,715,000	66,316,000	127,624,000	61,527,000	115,947,000	61,474,000	2,824,577,000	3,267,600,000	3,107,912,000	3,245,000	3,299,000	3,715,000
Available-for-sale Securities, Gross Unrealized Gains	98,609,000	101,898,000	98,609,000	101,898,000	100,416,000	28,000	358,000	590,000	17,003,000	22,865,000	16,426,000	61,160,000	53,129,000	61,416,000	233,000	17,836,000	22,058,000	23,327,000	0	82,000	139,000	2,349,000	1,648,000	0	276,000	0	98,609,000	100,416,000	101,898,000	0	0	0
Available-for-sale Securities, Gross Unrealized Losses	(14,438,000)	(15,479,000)	(14,438,000)	(15,479,000)	(17,762,000)	0	0	(20,000)	(21,000)	(50,000)	(125,000)	0	(131,000)	(2,000)	0	(383,000)	(55,000)	(45,000)	0	0	0	0	(145,000)	(14,034,000)	(17,381,000)	(15,287,000)	(14,438,000)	(17,762,000)	(15,479,000)	0	0	0
Available-for-sale	2,911,993,000	3,198,046,000	2,911,993,000	3,198,046,000	3,353,553,000	35,137,000	123,069,000	203,718,000	258,418,000	357,731,000	314,441,000	1,277,831,000	1,460,343,000	1,481,222,000	15,667,000	1,205,525,000	1,137,835,000	1,103,909,000	12,000	43,307,000	44,854,000	68,665,000	129,127,000	47,493,000	98,842,000	46,187,000	2,908,748,000	3,350,254,000	3,194,331,000	3,245,000	3,299,000	3,715,000
Securities held to maturity
Held-to-maturity Securities, Amortized Cost		92,214,000		92,214,000	82,764,000																												97,165,000	129,265,000	98,961,000	33,149,000	262,091,000	82,764,000	92,214,000
Held-to-maturity Securities, Unrecognized Holding Gain	10,623,000	2,707,000	10,623,000	2,707,000	2,348,000																												1,435,000	396,000	1,054,000	792,000	6,946,000	2,348,000	2,707,000
Held-to-maturity Securities, Unrecognized Holding Loss	(17,000)	0	(17,000)	0	0																												0	0	0	0	(17,000)	0	0
Held-to-maturity Securities, Fair Value		94,921,000		94,921,000	85,112,000																												98,600,000	129,661,000	100,015,000	33,941,000	269,020,000	85,112,000	94,921,000	631,237,000	94,921,000	85,112,000
Held-to-maturity Securities	$ 620,631,000	$ 92,214,000	$ 620,631,000	$ 92,214,000	$ 82,764,000