Securities Available for Sale and Held to Maturity (1) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	$ 452,008		$ 25,345
Estimated Fair Value, 12 Months or More	573		16,339
Estimated Fair Value, Total	452,581		41,684
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(1,677)		(57)
Gross Unrealized (Losses), 12 Months or More	(1)		(154)
Gross Unrealized (Losses), Total	(1,678)		(211)
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairments	0	0
Gains (losses) on investments [Abstract]
Gross realized gains	204	1,050
Securities Available for Sale, Amortized Cost [Abstract]
Due in one year or less	12,298
Due after one year through five years	106,600
Due after five years through ten years	389,757
Due after ten years	258,046
Total amortized cost, before Mortgage-backed securities	766,701
Mortgage-backed securities	2,704,583
Total, Securities Available for Sale, Amortized Cost	3,471,284
Securities Available for Sale, Estimated Fair Value [Abstract]
Due in one year or less	12,349
Due after one year through five years	110,902
Due after five years through ten years	399,690
Due after ten years	263,053
Total, Estimated Fair Value, before Mortgage-backed securities	785,994
Mortgage-backed securities	2,760,089
Total, Securities Available for Sale, Estimated Fair Value	3,546,083		2,657,745
Securities Held to Maturity, Amortized Cost [Abstract]
Due in one year or less	1,622
Due after one year through five years	15,450
Due after five years through ten years	14,772
Due after ten years	1,227
Total, Amortized Cost, before Mortgage-backed securities	33,071
Mortgage-backed securities	40,595
Total, Securities Held to Maturity, Amortized Cost	73,666		42,188
Securities Held to Maturity, Estimated Fair Value [Abstract]
Due in one year or less	1,634
Due after one year through five years	16,744
Due after five years through ten years	17,456
Due after ten years	1,295
Total, Estimated Fair Value, before Mortgage-backed securities	37,129
Mortgage-backed securities	40,967
Total, Securities Held to Maturity, Estimated Fair Value	78,096
Available-for-sale Securities [Member]
Gains (losses) on investments [Abstract]
Proceeds from calls and sales of securities	35,748	0
Gross realized gains	204	1,050
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	11,007
Estimated Fair Value, 12 Months or More	0
Estimated Fair Value, Total	11,007
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(119)
Gross Unrealized (Losses), 12 Months or More	0
Gross Unrealized (Losses), Total	(119)
U.S. Government Agency Obligations Issued by U.S. Government Sponsored Agencies [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	39,920
Estimated Fair Value, 12 Months or More	0
Estimated Fair Value, Total	39,920
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(186)
Gross Unrealized (Losses), 12 Months or More	0
Gross Unrealized (Losses), Total	(186)
Obligations of States and Political Subdivisions [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	3,689		5,878
Estimated Fair Value, 12 Months or More	573		0
Estimated Fair Value, Total	4,262		5,878
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(16)		(16)
Gross Unrealized (Losses), 12 Months or More	(1)		0
Gross Unrealized (Losses), Total	(17)		(16)
Residential Mortgage Pass Through Securities Guaranteed by GNMA [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	30,062
Estimated Fair Value, 12 Months or More	0
Estimated Fair Value, Total	30,062
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(190)
Gross Unrealized (Losses), 12 Months or More	0
Gross Unrealized (Losses), Total	(190)
Residential Mortgage Pass Through Securities Issued by FNMA and FHLMC [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	39,551
Estimated Fair Value, 12 Months or More	0
Estimated Fair Value, Total	39,551
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(18)
Gross Unrealized (Losses), 12 Months or More	0
Gross Unrealized (Losses), Total	(18)
Other Residential Mortgage Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	263,436		3,055
Estimated Fair Value, 12 Months or More	0		0
Estimated Fair Value, Total	263,436		3,055
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(775)		(20)
Gross Unrealized (Losses), 12 Months or More	0		0
Gross Unrealized (Losses), Total	(775)		(20)
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months	64,343		0
Estimated Fair Value, 12 Months or More	0		16,339
Estimated Fair Value, Total	64,343		16,339
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months	(373)		0
Gross Unrealized (Losses), 12 Months or More	0		(154)
Gross Unrealized (Losses), Total	(373)		(154)
Asset-backed Securities [Member]
Fair value [Abstract]
Estimated Fair Value, Less than 12 Months			16,412
Estimated Fair Value, 12 Months or More			0
Estimated Fair Value, Total			16,412
Gross unrealized losses [Abstract]
Gross Unrealized (Losses), Less than 12 Months			(21)
Gross Unrealized (Losses), 12 Months or More			0
Gross Unrealized (Losses), Total			$ (21)