Investment Securities (Gross Unrealized Loss Table) (Details) $ in Thousands	Mar. 31, 2016 USD ($) securities	Dec. 31, 2015 USD ($) securities	Mar. 31, 2015 USD ($)
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 281,941	$ 1,849,320	$ 245,893
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (6,865)	$ (19,569)	$ (1,647)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	46	180	46
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 793,054	$ 913,649	$ 1,172,260
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (27,516)	$ (37,458)	$ (29,123)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	79	91	114
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,074,995	$ 2,762,969	$ 1,418,153
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	34,381	57,027	30,770
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	17,759	370,605	90,604
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (284)	$ (2,916)	$ (1,287)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	10	58	30
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 1,033,743	$ 1,171,297	$ 1,389,498
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (15,647)	$ (40,433)	$ (30,046)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	74	79	83
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,051,502	$ 1,541,902	$ 1,480,102
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	(15,931)	(43,349)	(31,333)
US Government Agencies Debt Securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		2,498
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		$ (2)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		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, Accumulated Loss		$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 2,498
Available-for-sale Securities, Continuous Unrealized Loss Position, Total		2
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0		$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0		$ 24,822
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0		$ (178)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	0		1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 0		$ 24,822
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	0		(178)
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	2,880	10,178	14,380
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (14)	$ (37)	$ (117)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	6	20	23
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 1,899	$ 5,899	$ 6,004
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (20)	$ (167)	$ (269)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	4	9	10
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 4,779	$ 16,077	$ 20,384
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	34	204	386
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	4,491	18,465	38,202
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (21)	$ (224)	$ (1,093)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	9	21	26
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 7,793	$ 4,174	$ 4,448
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (241)	$ (38)	$ (54)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	10	6	6
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 12,284	$ 22,639	$ 42,650
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	(262)	(262)	(1,147)
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	171	328,156	74,517
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ (3,026)	$ (360)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	2	27	5
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 32,960	$ 95,895	$ 108,052
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (253)	$ (2,428)	$ (1,589)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	3	7	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 33,131	$ 424,051	$ 182,569
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	253	5,454	1,949
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	85,738	28,386
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ (715)	$ (123)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	6	2
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 62,997	$ 97,880	$ 110,329
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (212)	$ (2,284)	$ (1,554)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	4	6	6
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 62,997	$ 183,618	$ 138,715
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	(212)	(2,999)	(1,677)
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	0	107,074	49,129
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ (1,447)	$ (175)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	0	15	7
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 12,595	$ 12,401	$ 17,690
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (252)	$ (576)	$ (486)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	1	1	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 12,595	$ 119,475	$ 66,819
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	252	2,023	661
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	13,268	34,833	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (263)	$ (346)	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	1	6	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 9,438	$ 9,269	$ 9,554
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (3)	$ (228)	$ (108)
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	$ 22,706	$ 44,102	$ 9,554
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	(266)	(574)	(108)
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	96,691	1,130,779	70,574
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (568)	$ (10,587)	$ (762)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	6	78	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 552,785	$ 597,403	$ 745,621
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (7,491)	$ (19,560)	$ (13,095)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	46	49	53
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 649,476	$ 1,728,182	$ 816,195
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	8,059	30,147	13,857
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	140,514	19,016
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ (1,225)	$ (71)
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	12	1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 873,299	$ 941,982	$ 1,095,375
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (14,257)	$ (34,656)	$ (24,775)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	52	55	56
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 873,299	$ 1,082,496	$ 1,114,391
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	(14,257)	(35,881)	(24,846)
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	32,200	113,825	13,206
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (107)	$ (893)	$ (24)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	5	12	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 22,464	$ 23,400	$ 61,132
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (184)	$ (376)	$ (358)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	2	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 54,664	$ 137,225	$ 74,338
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	291	1,269	382
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	71,812	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ (384)	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions	0	7	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 80,216	$ 117,992	$ 144,970
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (934)	$ (3,227)	$ (3,377)
Held to Maturity Securities in Unrealized Loss Positions Twelve Months or Longer Qualitative Disclosure Number of Positions	7	11	13
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 80,216	$ 189,804	$ 144,970
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total	(934)	(3,611)	(3,377)
Collateralized Loan Obligations
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	149,999	151,810	24,087
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (6,176)	$ (3,576)	$ (209)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	27	26	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 121,596	$ 126,422	$ 181,498
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (6,348)	$ (4,870)	$ (3,922)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	15	15	27
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 271,595	$ 278,232	$ 205,585
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	12,524	8,446	4,131
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, Accumulated Loss	$ 0	$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	0	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 48,755	$ 52,229	$ 52,263
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (12,968)	$ (9,481)	$ (9,404)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	8	8	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 48,755	$ 52,229	$ 52,263
Available-for-sale Securities, Continuous Unrealized Loss Position, Total	$ 12,968	9,481	9,404
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		19,243	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		$ (22)	$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions		6	0
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, Accumulated Loss		$ 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		$ 19,243	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total		(22)	0
US Treasury Securities
Securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		5,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		$ (1)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		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, Accumulated Loss		$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 5,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Total		$ 1
Securities held to maturity
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value			5,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss			$ 0
Held to Maturity Securities in Unrealized Loss Positions Less than Twelve Months Qualitative Disclosure Number of Positions			1
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, Accumulated Loss			$ 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			$ 5,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total			$ 0