Investment Securities (Gross Unrealized Loss Table) (Details) $ in Thousands	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 508,560	$ 424,916	$ 638,746
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (4,553)	$ (2,807)	$ (5,848)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	78	53	57.000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 971,439	$ 1,485,458	$ 1,480,671
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (23,529)	$ (49,824)	$ (58,762)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	95	162	163
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,479,999	$ 1,910,374	$ 2,119,417
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(28,082)	(52,631)	(64,610)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	110,448	125,775	229,599
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (1,205)	$ (277)	$ (1,657)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	54	30	51.000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 1,265,766	$ 1,577,797	$ 1,657,757
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (25,923)	$ (49,520)	$ (71,229)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	81	108	129.000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,376,214	$ 1,703,572	$ 1,887,356
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(27,128)	(49,797)	(72,886)
US Government Agencies Debt Securities
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ 0	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 24,959	$ 24,463	$ 24,244
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (41)	$ (537)	$ (756)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	1	1	1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 24,959	$ 24,463	$ 24,244
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(41)	(537)	(756)
U.S. States and political subdivisions debt securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	11,972	5,637	5,298
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (149)	$ (11)	$ (10)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	23	11	5
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 5,810	$ 22,528	$ 22,729
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (262)	$ (455)	$ (597)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	9	36	37
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 17,782	$ 28,165	$ 28,027
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(411)	(466)	(607)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	53,159	9,085	16,255
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (928)	$ (17)	$ (78)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	50	9	20
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 4,452	$ 18,371	$ 29,783
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (49)	$ (174)	$ (374)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	6	21	38
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 57,611	$ 27,456	$ 46,038
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(977)	(191)	(452)
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	153,059	50,126	25,456
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (422)	$ (182)	$ (86)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	14	5	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 100,526	$ 199,773	$ 248,946
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (1,293)	$ (3,036)	$ (6,960)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	8	14	19
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 253,585	$ 249,899	$ 274,402
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(1,715)	(3,218)	(7,046)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	12,516	0	10,549
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (70)	$ 0	$ (64)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	0	1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 102,426	$ 185,361	$ 188,704
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (1,179)	$ (3,045)	$ (5,928)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	6	10	10
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 114,942	$ 185,361	$ 199,253
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(1,249)	(3,045)	(5,992)
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	9,744	12,284	9,095
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (46)	$ (55)	$ (56)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	2	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 12,676	$ 45,485	$ 45,208
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (434)	$ (1,316)	$ (1,832)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	1	6	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 22,420	$ 57,769	$ 54,303
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(480)	(1,371)	(1,888)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	9,950	26,346
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ (4)	$ (110)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	2	5
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 9,543	$ 16,735	$ 23,788
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (11)	$ (325)	$ (566)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	1	2	3
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 9,543	$ 26,685	$ 50,134
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(11)	(329)	(676)
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	122,235	243,970	436,857
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (490)	$ (906)	$ (3,528)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	11	15	29
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 665,809	$ 905,478	$ 890,497
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (12,026)	$ (25,319)	$ (35,447)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	52	64	63
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 788,044	$ 1,149,448	$ 1,327,354
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(12,516)	(26,225)	(38,975)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	44,773	28,333	121,516
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (207)	$ (149)	$ (1,195)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	3	3	8
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 995,866	$ 1,161,297	$ 1,208,939
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (22,225)	$ (38,726)	$ (55,065)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	55	58	60
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,040,639	$ 1,189,630	$ 1,330,455
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(22,432)	(38,875)	(56,260)
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	8,800	31,375	61,703
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (12)	$ (229)	$ (264)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	4	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 60,177	$ 67,169	$ 67,029
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (278)	$ (1,176)	$ (1,529)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	6	7	7
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 68,977	$ 98,544	$ 128,732
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(290)	(1,405)	(1,793)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	41,474	8,026
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ (55)	$ (30)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	3	1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 128,520	$ 171,570	$ 182,299
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (2,418)	$ (6,713)	$ (8,540)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	12	16	17
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 128,520	$ 213,044	$ 190,325
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(2,418)	(6,768)	(8,570)
Collateralized Loan Obligations
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	202,750	79,042	100,337
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (3,434)	$ (1,406)	$ (1,904)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	28	15	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 71,904	$ 193,687	$ 151,668
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (2,078)	$ (8,207)	$ (5,353)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	11	27	23
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 274,654	$ 272,729	$ 252,005
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(5,512)	(9,613)	(7,257)
Corporate debt securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ 0	$ 0
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 54,537	$ 51,338	$ 54,594
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (7,158)	$ (10,315)	$ (7,044)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	8	8	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 54,537	$ 51,338	$ 54,594
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	$ (7,158)	(10,315)	(7,044)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		36,933	46,907
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ (52)	$ (180)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions		13	16
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 0	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 0	$ 0
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions		0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value		$ 36,933	$ 46,907
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses		(52)	$ (180)
US Treasury Securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		2,482
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ (18)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions		1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 0
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period		$ 0
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 2,482
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period		$ (18)