Non-Covered Loans and Allowance for Non-Covered Loan Losses - Allowance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Changes in the allowance for loan losses
Balance, beginning of period			$ 60,957
Provision (recovery) for loan losses	$ (371)	$ 1,260	(1,838)	$ 8,818
Balance, end of period	58,861		58,861
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans					$ 6,796,278	$ 6,273,669
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	58,861		60,957		58,861	60,957
Noncovered
Changes in the allowance for loan losses
Balance, beginning of period	59,996	59,208	60,957	54,186
Provision (recovery) for loan losses	307	479	(456)	6,581
Loans charged off	(1,846)	(1,305)	(5,335)	(3,582)
Recoveries on charged off loans	404	397	3,695	1,594
Balance, end of period	58,861	58,779	58,861	58,779
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment					26,604	31,212
Loans collectively evaluated for impairment					6,737,121	6,205,253
Total loans					6,796,278	6,273,669
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance					3,570	1,390
Loans collectively evaluated for impairment, allowance					53,947	57,529
Total loans, allowance	59,996	59,208	60,957	54,186	58,861	60,957
Noncovered | Commercial and industrial
Changes in the allowance for loan losses
Balance, beginning of period	23,517	21,834	23,674	21,369
Provision (recovery) for loan losses	(242)	2,165	(123)	3,376
Loans charged off	(1,820)	(1,264)	(5,236)	(3,070)
Recoveries on charged off loans	366	280	3,506	1,340
Balance, end of period	21,821	23,015	21,821	23,015
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment					17,255	16,819
Loans collectively evaluated for impairment					1,697,929	1,658,287
Total loans					1,722,097	1,681,205
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance					2,739	365
Loans collectively evaluated for impairment, allowance					19,060	23,220
Total loans, allowance	23,517	21,834	23,674	21,369	21,821	23,674
Noncovered | Real estate
Changes in the allowance for loan losses
Balance, beginning of period	28,584	28,734	28,775	25,236
Provision (recovery) for loan losses	450	(1,278)	186	2,424
Loans charged off		(5)	(30)	(305)
Recoveries on charged off loans	31	88	134	184
Balance, end of period	29,065	27,539	29,065	27,539
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment					5,947	13,782
Loans collectively evaluated for impairment					3,350,887	2,968,202
Total loans					3,381,757	3,011,524
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance					782	932
Loans collectively evaluated for impairment, allowance					27,073	26,127
Total loans, allowance	28,584	28,734	28,775	25,236	29,065	28,775
Noncovered | Construction and land development
Changes in the allowance for loan losses
Balance, beginning of period	7,271	7,645	7,844	7,002
Provision (recovery) for loan losses	443	144	(130)	796
Loans charged off		(3)		(13)
Recoveries on charged off loans		4		5
Balance, end of period	7,714	7,790	7,714	7,790
Loan portfolio distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment					3,402	611
Loans collectively evaluated for impairment					1,048,300	960,556
Total loans					1,052,409	962,605
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans individually evaluated for impairment, allowance					49	93
Loans collectively evaluated for impairment, allowance					7,553	7,536
Total loans, allowance	7,271	7,645	7,844	7,002	7,714	7,844
Noncovered | Consumer
Changes in the allowance for loan losses
Balance, beginning of period	207	524	311	424
Provision (recovery) for loan losses	27	(147)	(82)	74
Loans charged off	(26)	(33)	(69)	(194)
Recoveries on charged off loans	7	25	55	65
Balance, end of period	215	369	215	369
Loan portfolio distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment					46,729	40,319
Total loans					46,739	40,446
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment, allowance					215	293
Total loans, allowance	207	524	311	424	215	311
Noncovered | Broker-dealer
Changes in the allowance for loan losses
Balance, beginning of period	417	471	353	155
Provision (recovery) for loan losses	(371)	(405)	(307)	(89)
Balance, end of period	46	66	46	66
Loan portfolio distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment					593,276	577,889
Total loans					593,276	577,889
Allowance for loan losses distributed by portfolio segment and impairment methodology
Loans collectively evaluated for impairment, allowance					46	353
Total loans, allowance	417	$ 471	353	$ 155	46	353
Noncovered | PCI loans
Changes in the allowance for loan losses
Balance, beginning of period			2,038
Balance, end of period	1,344		1,344
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans					32,553	37,204
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	1,344		2,038		1,344	2,038
Noncovered | PCI loans | Commercial and industrial
Changes in the allowance for loan losses
Balance, beginning of period			89
Balance, end of period	22		22
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans					6,913	6,099
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	22		89		22	89
Noncovered | PCI loans | Real estate
Changes in the allowance for loan losses
Balance, beginning of period			1,716
Balance, end of period	1,210		1,210
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans					24,923	29,540
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	1,210		1,716		1,210	1,716
Noncovered | PCI loans | Construction and land development
Changes in the allowance for loan losses
Balance, beginning of period			215
Balance, end of period	112		112
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans					707	1,438
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance	$ 112		215		112	215
Noncovered | PCI loans | Consumer
Changes in the allowance for loan losses
Balance, beginning of period			18
Loan portfolio distributed by portfolio segment and impairment methodology
Total loans					$ 10	127
Allowance for loan losses distributed by portfolio segment and impairment methodology
Total loans, allowance			$ 18			$ 18