Non-Covered Loans and Allowance for Non-Covered Loan Losses - Internal Risk Grades (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Internal risk grades of non-covered loans
Total loans	$ 6,384,660	$ 6,273,669
Noncovered
Internal risk grades of non-covered loans
Total loans	6,384,660	6,273,669
Noncovered | Pass
Internal risk grades of non-covered loans
Total loans	6,210,220	6,092,219
Noncovered | Special Mention
Internal risk grades of non-covered loans
Total loans	11,340	27,260
Noncovered | Substandard
Internal risk grades of non-covered loans
Total loans	136,435	116,986
Noncovered | Secured
Internal risk grades of non-covered loans
Total loans	1,535,133	1,558,316
Noncovered | Secured | Pass
Internal risk grades of non-covered loans
Total loans	1,462,355	1,483,502
Noncovered | Secured | Special Mention
Internal risk grades of non-covered loans
Total loans	6,600	17,354
Noncovered | Secured | Substandard
Internal risk grades of non-covered loans
Total loans	61,123	51,361
Noncovered | Unsecured
Internal risk grades of non-covered loans
Total loans	120,298	122,889
Noncovered | Unsecured | Pass
Internal risk grades of non-covered loans
Total loans	119,289	121,774
Noncovered | Unsecured | Substandard
Internal risk grades of non-covered loans
Total loans	1,009	1,115
Noncovered | Secured by Commercial Properties
Internal risk grades of non-covered loans
Total loans	2,317,410	2,235,643
Noncovered | Secured by Commercial Properties | Pass
Internal risk grades of non-covered loans
Total loans	2,233,481	2,154,595
Noncovered | Secured by Commercial Properties | Special Mention
Internal risk grades of non-covered loans
Total loans	4,740	7,647
Noncovered | Secured by Commercial Properties | Substandard
Internal risk grades of non-covered loans
Total loans	62,427	53,726
Noncovered | Secured by Residential Properties
Internal risk grades of non-covered loans
Total loans	825,086	775,881
Noncovered | Secured by Residential Properties | Pass
Internal risk grades of non-covered loans
Total loans	809,996	756,091
Noncovered | Secured by Residential Properties | Substandard
Internal risk grades of non-covered loans
Total loans	11,161	9,925
Noncovered | Residential Construction Loans
Internal risk grades of non-covered loans
Total loans	209,655	177,252
Noncovered | Residential Construction Loans | Pass
Internal risk grades of non-covered loans
Total loans	209,655	177,252
Noncovered | Commercial construction loans and land development
Internal risk grades of non-covered loans
Total loans	738,654	785,353
Noncovered | Commercial construction loans and land development | Pass
Internal risk grades of non-covered loans
Total loans	737,143	780,905
Noncovered | Commercial construction loans and land development | Special Mention
Internal risk grades of non-covered loans
Total loans		2,259
Noncovered | Commercial construction loans and land development | Substandard
Internal risk grades of non-covered loans
Total loans	592	751
Noncovered | Consumer
Internal risk grades of non-covered loans
Total loans	38,262	40,446
Noncovered | Consumer | Pass
Internal risk grades of non-covered loans
Total loans	38,139	40,211
Noncovered | Consumer | Substandard
Internal risk grades of non-covered loans
Total loans	123	108
Noncovered | Broker-dealer
Internal risk grades of non-covered loans
Total loans	600,162	577,889
Noncovered | Broker-dealer | Pass
Internal risk grades of non-covered loans
Total loans	600,162	577,889
Noncovered | PCI loans
Internal risk grades of non-covered loans
Total loans	26,665	37,204
Noncovered | PCI loans | Secured
Internal risk grades of non-covered loans
Total loans	5,055	6,099
Noncovered | PCI loans | Secured by Commercial Properties
Internal risk grades of non-covered loans
Total loans	16,762	19,675
Noncovered | PCI loans | Secured by Residential Properties
Internal risk grades of non-covered loans
Total loans	3,929	9,865
Noncovered | PCI loans | Commercial construction loans and land development
Internal risk grades of non-covered loans
Total loans	$ 919	1,438
Noncovered | PCI loans | Consumer
Internal risk grades of non-covered loans
Total loans		$ 127