Securities Available for Sale and Held to Maturity (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Available for sale securities [Abstract]
Amortized cost	$ 2,353,864	$ 2,189,005
Gross unrealized gains	37,355	31,979
Gross unrealized (losses)	(14,788)	(26,830)
Estimated fair value	2,376,431	2,194,154
Held to maturity securities [Abstract]
Amortized cost	1,156,790	1,168,728
Gross unrealized gains	10,693	3,063
Gross unrealized (losses)	(4,612)	(20,958)
Estimated fair value	1,162,871	1,150,833
US Treasury Securities [Member]
Held to maturity securities [Abstract]
Amortized cost	0	0
Gross unrealized gains	0	0
Gross unrealized (losses)	0	0
Estimated fair value	0	0
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member]
Held to maturity securities [Abstract]
Amortized cost	0	0
Gross unrealized gains	0	0
Gross unrealized (losses)	0	0
Estimated fair value	0	0
U.S. Government Agency Obligations Issued by U.S. Government Sponsored Agencies [Member]
Held to maturity securities [Abstract]
Amortized cost	100,563	100,159
Gross unrealized gains	2,201	0
Gross unrealized (losses)	0	(1,580)
Estimated fair value	102,764	98,579
Obligations of States and Political Subdivisions [Member]
Held to maturity securities [Abstract]
Amortized cost	65,193	65,987
Gross unrealized gains	3,674	2,806
Gross unrealized (losses)	0	(281)
Estimated fair value	68,867	68,512
Residential Mortgage Pass Through Securities Guaranteed by GNMA [Member]
Held to maturity securities [Abstract]
Amortized cost	13,959	9,433
Gross unrealized gains	367	142
Gross unrealized (losses)	(2)	(72)
Estimated fair value	14,324	9,503
Residential Mortgage Pass Through Securities Issued by FNMA and FHLMC [Member]
Held to maturity securities [Abstract]
Amortized cost	12,165	12,724
Gross unrealized gains	267	30
Gross unrealized (losses)	0	(162)
Estimated fair value	12,432	12,592
Other Residential Mortgage Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Held to maturity securities [Abstract]
Amortized cost	822,444	837,393
Gross unrealized gains	3,092	0
Gross unrealized (losses)	(3,208)	(15,072)
Estimated fair value	822,328	822,321
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Held to maturity securities [Abstract]
Amortized cost	142,466	143,032
Gross unrealized gains	1,092	85
Gross unrealized (losses)	(1,402)	(3,791)
Estimated fair value	142,156	139,326
Asset-Backed Securities and Structured Financial Products [Member]
Held to maturity securities [Abstract]
Amortized cost	0	0
Gross unrealized gains	0	0
Gross unrealized (losses)	0	0
Estimated fair value	0	0
US Treasury Securities [Member]
Available for sale securities [Abstract]
Amortized cost	100	501
Gross unrealized gains	0	1
Gross unrealized (losses)	0	0
Estimated fair value	100	502
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member]
Available for sale securities [Abstract]
Amortized cost	117,890	129,653
Gross unrealized gains	851	1,125
Gross unrealized (losses)	(1,252)	(1,485)
Estimated fair value	117,489	129,293
U.S. Government Agency Obligations Issued by U.S. Government Sponsored Agencies [Member]
Available for sale securities [Abstract]
Amortized cost	40,706	40,681
Gross unrealized gains	158	19
Gross unrealized (losses)	(16)	(521)
Estimated fair value	40,848	40,179
Obligations of States and Political Subdivisions [Member]
Available for sale securities [Abstract]
Amortized cost	164,581	165,810
Gross unrealized gains	6,710	6,243
Gross unrealized (losses)	(62)	(315)
Estimated fair value	171,229	171,738
Residential Mortgage Pass Through Securities Guaranteed by GNMA [Member]
Available for sale securities [Abstract]
Amortized cost	12,955	14,099
Gross unrealized gains	554	459
Gross unrealized (losses)	(17)	(84)
Estimated fair value	13,492	14,474
Residential Mortgage Pass Through Securities Issued by FNMA and FHLMC [Member]
Available for sale securities [Abstract]
Amortized cost	219,987	239,880
Gross unrealized gains	5,304	3,147
Gross unrealized (losses)	(62)	(1,909)
Estimated fair value	225,229	241,118
Other Residential Mortgage Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Available for sale securities [Abstract]
Amortized cost	1,542,274	1,300,375
Gross unrealized gains	14,703	12,459
Gross unrealized (losses)	(13,358)	(22,093)
Estimated fair value	1,543,619	1,290,741
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Available for sale securities [Abstract]
Amortized cost	221,221	235,317
Gross unrealized gains	8,083	7,278
Gross unrealized (losses)	(21)	(423)
Estimated fair value	229,283	242,172
Asset-Backed Securities and Structured Financial Products [Member]
Available for sale securities [Abstract]
Amortized cost	34,150	62,689
Gross unrealized gains	992	1,248
Gross unrealized (losses)	0	0
Estimated fair value	$ 35,142	$ 63,937