Non-Covered Loans and Allowance for Non-Covered Loan Losses - Allowance (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Changes in the allowance for loan losses
Balance, beginning of period					$ 54,186
Provision charged to (recapture from) operations	$ 1,260		$ 3,990		8,818	$ 36,273
Balance, end of period	58,779				58,779
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans							$ 6,148,813	$ 5,843,499
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	58,779				54,186		58,779	54,186
Noncovered
Allowance for loan losses
Charge-off of single loan, currently in default				$ 24,500
Other noninterest income coverage provided by an insurance policy for forgery		$ 15,000
Changes in the allowance for loan losses
Balance, beginning of period	59,208		51,013		54,186	45,415
Provision charged to (recapture from) operations	479		4,719		6,581	37,098
Loans charged off	(1,305)		(3,618)		(3,582)	(31,788)
Recoveries on charged off loans	397		511		1,594	1,900
Balance, end of period	58,779	59,208	52,625	51,013	58,779	52,625
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment							31,659	15,144
Loans collectively evaluated for impairment							6,079,217	5,776,923
Total loans							6,148,813	5,843,499
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance							958	282
Loans collectively evaluated for impairment, allowance							55,723	50,807
Total loans, allowance	59,208	59,208	51,013	51,013	54,186	45,415	58,779	54,186
Noncovered | Commercial and industrial
Changes in the allowance for loan losses
Balance, beginning of period	21,834		20,720		21,369	19,845
Provision charged to (recapture from) operations	2,165		3,973		3,376	30,494
Loans charged off	(1,264)		(3,550)		(3,070)	(30,333)
Recoveries on charged off loans	280		295		1,340	1,432
Balance, end of period	23,015	21,834	21,438	20,720	23,015	21,438
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment							17,311	4,508
Loans collectively evaluated for impairment							1,711,925	1,683,273
Total loans							1,735,468	1,696,453
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance								115
Loans collectively evaluated for impairment, allowance							22,904	20,697
Total loans, allowance	21,834	21,834	20,720	20,720	21,369	19,845	23,015	21,369
Noncovered | Real estate
Changes in the allowance for loan losses
Balance, beginning of period	28,734		23,302		25,236	18,983
Provision charged to (recapture from) operations	(1,278)		(116)		2,424	5,333
Loans charged off	(5)		(1)		(305)	(1,299)
Recoveries on charged off loans	88		196		184	364
Balance, end of period	27,539	28,734	23,381	23,302	27,539	23,381
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment							13,722	9,704
Loans collectively evaluated for impairment							2,900,479	2,768,064
Total loans							2,944,155	2,816,767
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance							846
Loans collectively evaluated for impairment, allowance							24,987	23,129
Total loans, allowance	28,734	28,734	23,302	23,302	25,236	18,983	27,539	25,236
Noncovered | Construction and land development
Changes in the allowance for loan losses
Balance, beginning of period	7,645		6,288		7,002	6,064
Provision charged to (recapture from) operations	144		823		796	1,047
Loans charged off	(3)				(13)
Recoveries on charged off loans	4				5
Balance, end of period	7,790	7,645	7,111	6,288	7,790	7,111
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment							626	727
Loans collectively evaluated for impairment							939,414	782,656
Total loans							941,628	786,850
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance							112	167
Loans collectively evaluated for impairment, allowance							7,441	6,458
Total loans, allowance	7,645	7,645	6,288	6,288	7,002	6,064	7,790	7,002
Noncovered | Consumer
Changes in the allowance for loan losses
Balance, beginning of period	524		325		424	314
Provision charged to (recapture from) operations	(147)		228		74	243
Loans charged off	(33)		(67)		(194)	(155)
Recoveries on charged off loans	25		20		65	104
Balance, end of period	369	524	506	325	369	506
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment								205
Loans collectively evaluated for impairment							41,795	40,853
Total loans							41,958	41,352
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment, allowance							325	368
Total loans, allowance	524	524	325	325	424	314	369	424
Noncovered | Broker-dealer
Changes in the allowance for loan losses
Balance, beginning of period	471		378		155	209
Provision charged to (recapture from) operations	(405)		(189)		(89)	(19)
Loans charged off						(1)
Balance, end of period	66	471	189	378	66	189
Loan portfolio distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment							485,604	502,077
Total loans							485,604	502,077
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment, allowance							66	155
Total loans, allowance	471	$ 471	$ 378	$ 378	155	$ 209	66	155
Noncovered | PCI loans
Changes in the allowance for loan losses
Balance, beginning of period					3,097
Balance, end of period	2,098				2,098
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans							37,937	51,432
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	2,098				3,097		2,098	3,097
Noncovered | PCI loans | Commercial and industrial
Changes in the allowance for loan losses
Balance, beginning of period					557
Balance, end of period	111				111
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans							6,232	8,672
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	111				557		111	557
Noncovered | PCI loans | Real estate
Changes in the allowance for loan losses
Balance, beginning of period					2,107
Balance, end of period	1,706				1,706
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans							29,954	38,999
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	1,706				2,107		1,706	2,107
Noncovered | PCI loans | Construction and land development
Changes in the allowance for loan losses
Balance, beginning of period					377
Balance, end of period	237				237
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans							1,588	3,467
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	237				377		237	377
Noncovered | PCI loans | Consumer
Changes in the allowance for loan losses
Balance, beginning of period					56
Balance, end of period	44				44
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans							163	294
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	$ 44				$ 56		$ 44	$ 56