Securities (Details) $ in Thousands	Jun. 30, 2015 USD ($) Position	Dec. 31, 2014 USD ($) Position
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,118,270	$ 1,001,718
Unrealized gains	13,247	14,823
Unrealized losses	(2,268)	(3,370)
Estimated fair value	1,129,249	1,013,171
Amortized costs of securities available for sale pledged to secure public deposits	1,400,000	1,400,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	172,200	208,800
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	298,181	143,428
12 Months or Longer, Fair Value	42,966	244,836
Total, Fair Value	341,147	388,264
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(1,761)	(500)
12 months or longer Unrealized Losses	(507)	(2,870)
Total Unrealized Losses	$ (2,268)	$ (3,370)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	64	59
12 Months or Longer, Number of Positions | Position	26	58
Total, Number of Positions | Position	90	117
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 454,312	$ 454,361
Unrealized gains	2,353	2,721
Unrealized losses	(2,410)	(2,088)
Estimated fair value	454,255	454,994
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	129,010	69,566
12 Months or Longer, Fair Value	44,136	48,034
Total, Fair Value	173,146	117,600
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(890)	(165)
12 Months or Longer, Unrealized Losses	(1,520)	(1,923)
Total, Unrealized Losses	$ (2,410)	$ (2,088)
Unrealized Loss Position, Number of Positions [Abstract]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | Position	98	112
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater Than or Equal to One Year | Position	4	10
Total, Number of Positions | Position	102	122
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within one year	$ 13,981
From one to five years	412,442
From five to ten years	150,200
After ten years	528,775
Total, Amortized Cost	1,105,398
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	14,032
From one to five years	413,423
From five to ten years	152,606
After ten years	533,588
Total, Fair Value	1,113,649
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Within one year	24,317
From one to five years	15,730
From five to ten years	99,778
After ten years	314,487
Amortized cost	454,312	$ 454,361
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within one year	24,328
From one to five years	15,811
From five to ten years	99,818
After ten years	314,298
Total, Fair Value	454,255	454,994
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,005	23,041
Unrealized gains	9	70
Unrealized losses	0	0
Estimated fair value	10,014	23,111
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	397,197	332,193
Unrealized gains	759	327
Unrealized losses	(1,033)	(2,606)
Estimated fair value	396,923	329,914
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	146,403	66,528
12 Months or Longer, Fair Value	29,732	198,151
Total, Fair Value	176,135	264,679
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(765)	(226)
12 months or longer Unrealized Losses	(268)	(2,380)
Total Unrealized Losses	$ (1,033)	$ (2,606)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	13	8
12 Months or Longer, Number of Positions | Position	3	16
Total, Number of Positions | Position	16	24
State & Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 29,881	$ 37,035
Unrealized gains	505	587
Unrealized losses	(26)	(52)
Estimated fair value	30,360	37,570
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	6,184	8,818
12 Months or Longer, Fair Value	0	1,321
Total, Fair Value	6,184	10,139
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(26)	(42)
12 months or longer Unrealized Losses	0	(10)
Total Unrealized Losses	$ (26)	$ (52)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	14	33
12 Months or Longer, Number of Positions | Position	0	5
Total, Number of Positions | Position	14	38
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	$ 57,745	$ 10,400
12 Months or Longer, Fair Value	4,571	35,565
Total, Fair Value	62,316	45,965
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(439)	(36)
12 months or longer Unrealized Losses	(59)	(254)
Total Unrealized Losses	$ (498)	$ (290)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	28	10
12 Months or Longer, Number of Positions | Position	17	31
Total, Number of Positions | Position	45	41
Mortgage-backed Securities, Issued by US Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 333,292	$ 339,190
Unrealized gains	5,914	7,597
Unrealized losses	(439)	(224)
Estimated fair value	338,767	346,563
Mortgage-backed Securities, Issued by US Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	15,325	17,367
Unrealized gains	796	863
Unrealized losses	(59)	(66)
Estimated fair value	16,062	18,164
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	87,849	57,682
12 Months or Longer, Fair Value	5,452	6,598
Total, Fair Value	93,301	64,280
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(531)	(196)
12 months or longer Unrealized Losses	(38)	(74)
Total Unrealized Losses	$ (569)	$ (270)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	9	8
12 Months or Longer, Number of Positions | Position	4	4
Total, Number of Positions | Position	13	12
Government-sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 285,733	$ 199,837
Unrealized gains	1,966	1,828
Unrealized losses	(535)	(234)
Estimated fair value	287,164	201,431
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	33,965	40,237
Unrealized gains	428	497
Unrealized losses	(34)	(36)
Estimated fair value	34,359	40,698
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	12,872	12,818
Unrealized gains	2,870	3,054
Unrealized losses	(142)	(152)
Estimated fair value	15,600	15,720
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	0
12 Months or Longer, Fair Value	3,211	3,201
Total, Fair Value	3,211	3,201
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	0	0
12 months or longer Unrealized Losses	(142)	(152)
Total Unrealized Losses	$ (142)	$ (152)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	0	0
12 Months or Longer, Number of Positions | Position	2	2
Total, Number of Positions | Position	2	2
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	$ 9,907
12 Months or Longer, Fair Value	0
Total, Fair Value	9,907
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(142)
12 Months or Longer, Unrealized Losses	0
Total, Unrealized Losses	$ (142)
Unrealized Loss Position, Number of Positions [Abstract]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | Position	1
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater Than or Equal to One Year | Position	0
Total, Number of Positions | Position	1
Mortgage-Backed [Member] | Government-sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 10,049	$ 755
Unrealized gains	0	113
Unrealized losses	(142)	0
Estimated fair value	9,907	868
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	10,049	755
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	9,907	868
Mortgage-Backed [Member] | U.S. Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	695
Unrealized gains	118
Unrealized losses	0
Estimated fair value	813
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	695
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	813
State & Municipal [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	148,058	135,978
Unrealized gains	466	674
Unrealized losses	(442)	(123)
Estimated fair value	148,082	136,529
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	43,095	43,514
12 Months or Longer, Fair Value	0	1,619
Total, Fair Value	43,095	45,133
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(442)	(116)
12 Months or Longer, Unrealized Losses	0	(7)
Total, Unrealized Losses	$ (442)	$ (123)
Unrealized Loss Position, Number of Positions [Abstract]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | Position	89	110
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater Than or Equal to One Year | Position	0	6
Total, Number of Positions | Position	89	116
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	$ 148,058	$ 135,978
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	148,082	136,529
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	76,008	26,052
12 Months or Longer, Fair Value	44,136	46,415
Total, Fair Value	120,144	72,467
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(306)	(49)
12 Months or Longer, Unrealized Losses	(1,520)	(1,916)
Total, Unrealized Losses	$ (1,826)	$ (1,965)
Unrealized Loss Position, Number of Positions [Abstract]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | Position	8	2
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater Than or Equal to One Year | Position	4	4
Total, Number of Positions | Position	12	6
Collateralized Mortgage Obligations [Member] | Government-sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 295,510	$ 317,628
Unrealized gains	1,769	1,934
Unrealized losses	(1,826)	(1,965)
Estimated fair value	295,453	317,597
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	295,510	317,628
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	$ 295,453	$ 317,597