Investment Securities (Unrealized Position - Less than 12 Mos., 12 Mos. or Longer) (Details 4) $ in Thousands	Sep. 30, 2015 USD ($) security	Dec. 31, 2014 USD ($)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	$ 225,225	$ 260,475
Less Than 12 Months, Gross Unrealized Losses	(2,075)	(1,677)
12 Months or Longer, Fair Value	260,957	470,871
12 Months or Longer, Gross Unrealized Losses	(5,900)	(13,608)
Total Fair Value	486,182	731,346
Total Gross Unrealized Losses	(7,975)	(15,285)
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	422,118	567,527
Less Than 12 Months, Gross Unrealized Losses	(3,140)	(1,884)
12 Months or Longer, Fair Value	570,499	1,243,333
12 Months or Longer, Gross Unrealized Losses	(10,014)	(27,159)
Total Fair Value	992,617	1,810,860
Total Gross Unrealized Losses	$ (13,154)	(29,043)
Number of investment securities that were in an unrealized loss position | security	125
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	$ 33,551	1,729
Less Than 12 Months, Gross Unrealized Losses	(156)	(2)
12 Months or Longer, Fair Value	5,072	5,546
12 Months or Longer, Gross Unrealized Losses	(9)	(38)
Total Fair Value	38,623	7,275
Total Gross Unrealized Losses	(165)	(40)
Debt Securities Issued by States and Political Subdivisions
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	55,896	78,068
Less Than 12 Months, Gross Unrealized Losses	(412)	(305)
12 Months or Longer, Fair Value	0	94,543
12 Months or Longer, Gross Unrealized Losses	0	(1,140)
Total Fair Value	55,896	172,611
Total Gross Unrealized Losses	(412)	(1,445)
Debt Securities Issued by Corporations
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	101,626	73,829
Less Than 12 Months, Gross Unrealized Losses	(1,392)	(1,171)
12 Months or Longer, Fair Value	143,489	180,335
12 Months or Longer, Gross Unrealized Losses	(1,603)	(2,814)
Total Fair Value	245,115	254,164
Total Gross Unrealized Losses	(2,995)	(3,985)
Mortgage-Backed Securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	34,152	106,849
Less Than 12 Months, Gross Unrealized Losses	(115)	(199)
12 Months or Longer, Fair Value	112,396	190,447
12 Months or Longer, Gross Unrealized Losses	(4,288)	(9,616)
Total Fair Value	146,548	297,296
Total Gross Unrealized Losses	(4,403)	(9,815)
Residential - Government Agencies
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	34,152	3,025
Less Than 12 Months, Gross Unrealized Losses	(115)	(8)
12 Months or Longer, Fair Value	9,832	12,215
12 Months or Longer, Gross Unrealized Losses	(1,117)	(1,035)
Total Fair Value	43,984	15,240
Total Gross Unrealized Losses	(1,232)	(1,043)
Residential - U.S. Government-Sponsored Enterprises
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value		103,824
Less Than 12 Months, Gross Unrealized Losses		(191)
12 Months or Longer, Fair Value		0
12 Months or Longer, Gross Unrealized Losses		0
Total Fair Value		103,824
Total Gross Unrealized Losses		(191)
Commercial - Government Agencies
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0
12 Months or Longer, Fair Value	102,564	178,232
12 Months or Longer, Gross Unrealized Losses	(3,171)	(8,581)
Total Fair Value	102,564	178,232
Total Gross Unrealized Losses	(3,171)	(8,581)
Debt Securities Issued by the U.S. Treasury and Government Agencies
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value		70,016
Less Than 12 Months, Gross Unrealized Losses		(134)
12 Months or Longer, Fair Value		144,222
12 Months or Longer, Gross Unrealized Losses		(1,025)
Total Fair Value		214,238
Total Gross Unrealized Losses		(1,159)
Debt Securities Issued by Corporations
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	0	46,196
Less Than 12 Months, Gross Unrealized Losses	0	(349)
12 Months or Longer, Fair Value	74,246	82,109
12 Months or Longer, Gross Unrealized Losses	(823)	(3,093)
Total Fair Value	74,246	128,305
Total Gross Unrealized Losses	(823)	(3,442)
Mortgage-Backed Securities
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	422,118	451,315
Less Than 12 Months, Gross Unrealized Losses	(3,140)	(1,401)
12 Months or Longer, Fair Value	496,253	1,017,002
12 Months or Longer, Gross Unrealized Losses	(9,191)	(23,041)
Total Fair Value	918,371	1,468,317
Total Gross Unrealized Losses	$ (12,331)	$ (24,442)