Securities Available for Sale and Held to Maturity - Securities with Gross Unrealized Losses, Segregated by Length of Impairment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 2,033,477	$ 1,506,669
Estimated Fair Value, 12 Months or More	114,975	284,538
Estimated Fair Value, Total	2,148,452	1,791,207
Gross Unrealized (Losses), Less than 12 Months	(26,714)	(12,487)
Gross Unrealized (Losses), 12 Months or More	(3,793)	(7,772)
Gross Unrealized (Losses), Total	(30,507)	(20,259)
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	9,420	18,924
Estimated Fair Value, 12 Months or More	33,248	30,591
Estimated Fair Value, Total	42,668	49,515
Gross Unrealized (Losses), Less than 12 Months	(142)	(81)
Gross Unrealized (Losses), 12 Months or More	(783)	(653)
Gross Unrealized (Losses), Total	(925)	(734)
Obligations of States and Political Subdivisions [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	20,539	4,289
Estimated Fair Value, 12 Months or More	654	2,842
Estimated Fair Value, Total	21,193	7,131
Gross Unrealized (Losses), Less than 12 Months	(135)	(12)
Gross Unrealized (Losses), 12 Months or More	(5)	(20)
Gross Unrealized (Losses), Total	(140)	(32)
Residential Mortgage Pass-Through Securities Guaranteed by GNMA [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	43,615	20,300
Estimated Fair Value, 12 Months or More	222	1,863
Estimated Fair Value, Total	43,837	22,163
Gross Unrealized (Losses), Less than 12 Months	(822)	(222)
Gross Unrealized (Losses), 12 Months or More	(6)	(16)
Gross Unrealized (Losses), Total	(828)	(238)
Residential Mortgage Pass-Through Securities Issued by FNMA and FHLMC [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	588,352	82,177
Estimated Fair Value, 12 Months or More	0
Estimated Fair Value, Total	588,352	82,177
Gross Unrealized (Losses), Less than 12 Months	(10,582)	(313)
Gross Unrealized (Losses), 12 Months or More	0	0
Gross Unrealized (Losses), Total	(10,582)	(313)
Other Residential Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,127,501	1,135,533
Estimated Fair Value, 12 Months or More	76,196	238,152
Estimated Fair Value, Total	1,203,697	1,373,685
Gross Unrealized (Losses), Less than 12 Months	(12,722)	(8,832)
Gross Unrealized (Losses), 12 Months or More	(2,909)	(6,929)
Gross Unrealized (Losses), Total	(15,631)	(15,761)
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	244,050	238,668
Estimated Fair Value, 12 Months or More	4,655	11,090
Estimated Fair Value, Total	248,705	249,758
Gross Unrealized (Losses), Less than 12 Months	(2,311)	(2,902)
Gross Unrealized (Losses), 12 Months or More	(90)	(154)
Gross Unrealized (Losses), Total	$ (2,401)	(3,056)
Asset-Backed Securities and Structured Financial Products [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months		6,778
Estimated Fair Value, 12 Months or More		0
Estimated Fair Value, Total		6,778
Gross Unrealized (Losses), Less than 12 Months		(125)
Gross Unrealized (Losses), 12 Months or More		0
Gross Unrealized (Losses), Total		$ (125)