Securities Available for Sale and Held to Maturity - Amortized Cost and Estimated Fair Value of Available for Sale and Held to Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	$ 2,339,562	$ 2,352,013
Gross Unrealized Gains	20,164	34,131
Gross Unrealized (Losses)	(14,304)	(11,577)
Estimated Fair Value	2,345,422	2,374,567
Amortized Cost	1,187,818	1,170,685
Gross Unrealized Gains	13,504	15,156
Gross Unrealized (Losses)	(5,955)	(2,995)
Estimated Fair Value	1,195,367	1,182,846
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	68,314	79,788
Gross Unrealized Gains	555	694
Gross Unrealized (Losses)	(734)	(826)
Estimated Fair Value	68,135	79,656
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]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	258	32,725
Gross Unrealized Gains	23	170
Gross Unrealized (Losses)	0	(77)
Estimated Fair Value	281	32,818
Amortized Cost	101,782	100,971
Gross Unrealized Gains	3,282	2,631
Gross Unrealized (Losses)	0	0
Estimated Fair Value	105,064	103,602
Obligations of States and Political Subdivisions [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	134,719	157,001
Gross Unrealized Gains	3,922	5,325
Gross Unrealized (Losses)	(32)	(68)
Estimated Fair Value	138,609	162,258
Amortized Cost	55,892	63,505
Gross Unrealized Gains	2,918	3,398
Gross Unrealized (Losses)	0	0
Estimated Fair Value	58,810	66,903
Residential Mortgage Pass-Through Securities Guaranteed by GNMA [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	25,602	11,897
Gross Unrealized Gains	399	544
Gross Unrealized (Losses)	(189)	(14)
Estimated Fair Value	25,812	12,427
Amortized Cost	17,363	19,115
Gross Unrealized Gains	342	466
Gross Unrealized (Losses)	(49)	(16)
Estimated Fair Value	17,656	19,565
Residential Mortgage Pass-Through Securities Issued by FNMA and FHLMC [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	222,899	199,599
Gross Unrealized Gains	2,956	4,842
Gross Unrealized (Losses)	(313)	0
Estimated Fair Value	225,542	204,441
Amortized Cost	10,368	11,437
Gross Unrealized Gains	311	471
Gross Unrealized (Losses)	0	0
Estimated Fair Value	10,679	11,908
Other Residential Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	1,584,338	1,655,733
Gross Unrealized Gains	9,541	16,664
Gross Unrealized (Losses)	(11,019)	(10,564)
Estimated Fair Value	1,582,860	1,661,833
Amortized Cost	820,012	834,176
Gross Unrealized Gains	4,951	6,440
Gross Unrealized (Losses)	(4,742)	(1,916)
Estimated Fair Value	820,221	838,700
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	278,429	184,394
Gross Unrealized Gains	2,689	4,968
Gross Unrealized (Losses)	(1,892)	(28)
Estimated Fair Value	279,226	189,334
Amortized Cost	182,401	141,481
Gross Unrealized Gains	1,700	1,750
Gross Unrealized (Losses)	(1,164)	(1,063)
Estimated Fair Value	182,937	142,168
Asset-Backed Securities and Structured Financial Products [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost	25,003	30,776
Gross Unrealized Gains	79	924
Gross Unrealized (Losses)	(125)	0
Estimated Fair Value	24,957	31,700
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Estimated Fair Value	$ 0	0
US Treasury Securities [Member]
Schedule of Available for Sale Securities [Line Items]
Amortized Cost		100
Gross Unrealized Gains		0
Gross Unrealized (Losses)		0
Estimated Fair Value		100
Amortized Cost		0
Gross Unrealized Gains		0
Gross Unrealized (Losses)		0
Estimated Fair Value		$ 0

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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