Securities, Available for Sale (Details) $ in Thousands	Jun. 30, 2016 USD ($) Position	Dec. 31, 2015 USD ($) Position
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,249,478	$ 1,169,337
Unrealized gains	23,762	9,878
Unrealized losses	(1,644)	(4,671)
Estimated fair value	1,271,596	1,174,544
Amortized costs of securities available for sale pledged to secure public deposits	1,600,000	1,400,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	193,900	205,900
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	13,829	624,819
12 Months or Longer, Fair Value	6,009	29,822
Total, Fair Value	19,838	654,641
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(20)	(4,283)
12 months or longer Unrealized Losses	(1,624)	(388)
Total Unrealized Losses	$ (1,644)	$ (4,671)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	10	79
12 Months or Longer, Number of Positions | Position	9	12
Total, Number of Positions | Position	19	91
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within one year	$ 28,638
From one to five years	278,354
From five to ten years	154,190
After ten years	771,623
Total, Amortized Cost	1,232,805
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	28,768
From one to five years	281,204
From five to ten years	157,898
After ten years	784,918
Total, Fair Value	1,252,788
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	265,194	$ 312,580
Unrealized gains	1,641	203
Unrealized losses	0	(1,511)
Estimated fair value	266,835	311,272
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value		186,685
12 Months or Longer, Fair Value		19,801
Total, Fair Value		206,486
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses		(1,312)
12 months or longer Unrealized Losses		(199)
Total Unrealized Losses		$ (1,511)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position		15
12 Months or Longer, Number of Positions | Position		2
Total, Number of Positions | Position		17
State & Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	37,105	$ 31,208
Unrealized gains	537	446
Unrealized losses	(12)	(17)
Estimated fair value	37,630	31,637
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	2,664	4,599
12 Months or Longer, Fair Value	493	502
Total, Fair Value	3,157	5,101
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(10)	(14)
12 months or longer Unrealized Losses	(2)	(3)
Total Unrealized Losses	$ (12)	$ (17)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	6	7
12 Months or Longer, Number of Positions | Position	1	1
Total, Number of Positions | Position	7	8
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	$ 145	$ 177,270
12 Months or Longer, Fair Value	1,010	1,066
Total, Fair Value	1,155	178,336
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(1)	(1,068)
12 months or longer Unrealized Losses	(13)	(14)
Total Unrealized Losses	$ (14)	$ (1,082)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	2	33
12 Months or Longer, Number of Positions | Position	5	5
Total, Number of Positions | Position	7	38
Mortgage-backed Securities, Issued by US Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 379,583	$ 398,086
Unrealized gains	9,683	4,141
Unrealized losses	(1)	(1,068)
Estimated fair value	389,265	401,159
Mortgage-backed Securities, Issued by US Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	6,886	8,191
Unrealized gains	547	560
Unrealized losses	(13)	(14)
Estimated fair value	7,420	8,737
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	11,020	256,265
12 Months or Longer, Fair Value	0	5,218
Total, Fair Value	11,020	261,483
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(9)	(1,889)
12 months or longer Unrealized Losses	0	(54)
Total Unrealized Losses	$ (9)	$ (1,943)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions | Position	2	24
12 Months or Longer, Number of Positions | Position	0	2
Total, Number of Positions | Position	2	26
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 492,466	$ 364,936
Unrealized gains	6,942	931
Unrealized losses	(5)	(1,828)
Estimated fair value	499,403	364,039
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	51,571	40,699
Unrealized gains	668	348
Unrealized losses	(4)	(115)
Estimated fair value	52,235	40,932
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	16,673	13,637
Unrealized gains	3,744	3,249
Unrealized losses	(1,609)	(118)
Estimated fair value	18,808	16,768
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	0
12 Months or Longer, Fair Value	4,506	3,235
Total, Fair Value	4,506	3,235
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	0	0
12 months or longer Unrealized Losses	(1,609)	(118)
Total Unrealized Losses	$ (1,609)	$ (118)
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	3	2
Total, Number of Positions | Position	3	2