Investment Securities (Gross Unrealized Loss Table) (Details) $ in Thousands	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2014 USD ($)
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 1,057,236	$ 424,916	$ 472,977
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (10,569)	$ (2,807)	$ (5,046)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	139	53	55.000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 1,029,278	$ 1,485,458	$ 1,418,752
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (32,871)	$ (49,824)	$ (51,350)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	97	162	161.000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 2,086,514	$ 1,910,374	$ 1,891,729
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(43,440)	(52,631)	(56,396)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	305,627	125,775	187,242
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (3,233)	$ (277)	$ (1,434)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	127	30	64.000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 1,329,114	$ 1,577,797	$ 1,747,578
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (41,739)	$ (49,520)	$ (67,419)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	83	108	182.000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,634,741	$ 1,703,572	$ 1,934,820
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(44,972)	(49,797)	(68,853)
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	$ 24,677	$ 24,463	$ 24,293
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (323)	$ (537)	$ (707)
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	$ 24,677	$ 24,463	$ 24,293
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(323)	(537)	(707)
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	32,237	5,637	10,988
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (587)	$ (11)	$ (16)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	52	11	14
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 5,642	$ 22,528	$ 30,271
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (436)	$ (455)	$ (1,007)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	9	36	50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 37,879	$ 28,165	$ 41,259
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(1,023)	(466)	(1,023)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	98,867	9,085	59,958
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (1,872)	$ (17)	$ (334)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	112	9	56
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 4,430	$ 18,371	$ 66,557
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (70)	$ (174)	$ (919)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	6	21	90
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 103,297	$ 27,456	$ 126,515
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(1,942)	(191)	(1,253)
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	196,219	50,126	11,636
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (2,087)	$ (182)	$ (3)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	15	5	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 103,498	$ 199,773	$ 259,470
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (2,476)	$ (3,036)	$ (5,486)
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	$ 299,717	$ 249,899	$ 271,106
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(4,563)	(3,218)	(5,489)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	83,112	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (483)	$ 0	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	5	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 105,289	$ 185,361	$ 206,911
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (2,457)	$ (3,045)	$ (4,933)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	6	10	11
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 188,401	$ 185,361	$ 206,911
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(2,940)	(3,045)	(4,933)
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	96,573	12,284	5,105
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (1,457)	$ (55)	$ (4)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	14	2	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 17,335	$ 45,485	$ 45,739
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (690)	$ (1,316)	$ (1,519)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	2	6	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 113,908	$ 57,769	$ 50,844
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(2,147)	(1,371)	(1,523)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	7,263	9,950	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (41)	$ (4)	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	2	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 9,430	$ 16,735	$ 23,977
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (178)	$ (325)	$ (445)
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	$ 16,693	$ 26,685	$ 23,977
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(219)	(329)	(445)
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	596,646	243,970	279,311
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (4,398)	$ (906)	$ (2,358)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	42	15	19
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 706,376	$ 905,478	$ 904,821
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (19,910)	$ (25,319)	$ (32,491)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	53	64	60
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,303,022	$ 1,149,448	$ 1,184,132
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(24,308)	(26,225)	(34,849)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	111,360	28,333	127,284
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (835)	$ (149)	$ (1,100)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	8	3	8
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 1,042,351	$ 1,161,297	$ 1,241,883
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (34,190)	$ (38,726)	$ (53,163)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	56	58	60
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,153,711	$ 1,189,630	$ 1,369,167
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(35,025)	(38,875)	(54,263)
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	46,771	31,375	24,431
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (71)	$ (229)	$ (97)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	5	4	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 61,120	$ 67,169	$ 43,212
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (634)	$ (1,176)	$ (1,029)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	7	7	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 107,891	$ 98,544	$ 67,643
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(705)	(1,405)	(1,126)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	5,025	41,474	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (2)	$ (55)	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	3	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 142,937	$ 171,570	$ 183,957
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (4,521)	$ (6,713)	$ (7,252)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	13	16	17
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 147,962	$ 213,044	$ 183,957
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(4,523)	(6,768)	(7,252)
Collateralized Loan Obligations
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	84,565	79,042	141,506
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (1,204)	$ (1,406)	$ (2,568)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	10	15	19
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 86,082	$ 193,687	$ 81,749
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (1,259)	$ (8,207)	$ (1,684)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	11	27	12
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 170,647	$ 272,729	$ 223,255
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(2,463)	(9,613)	(4,252)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 0
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	0
Corporate debt securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	4,225	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ (765)	$ 0	$ 0
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 49,225	$ 51,338	$ 53,490
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ (7,466)	$ (10,315)	$ (8,134)
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	7	8	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 53,450	$ 51,338	$ 53,490
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	(8,231)	(10,315)	(8,134)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	36,933	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ (52)	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	13	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0	$ 0	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 0	$ 0	$ 0
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	0	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 0	$ 36,933	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	0	(52)	$ 0
US Treasury Securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	2,482
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ (18)
Available for Sale Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0	$ 0
available for sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss at end of period	$ 0	$ 0
Available for Sale Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 0	$ 2,482
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	0	$ (18)
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 0
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 0