Non-Covered Loans and Allowance for Non-Covered Loan Losses - Internal Risk Grades (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Internal risk grades of non-covered loans
Total loans	$ 6,148,813	$ 5,843,499
Noncovered
Internal risk grades of non-covered loans
Total loans	6,148,813	5,843,499
Noncovered | Pass
Internal risk grades of non-covered loans
Total loans	5,983,747	5,689,490
Noncovered | Special Mention
Internal risk grades of non-covered loans
Total loans	31,683	3,771
Noncovered | Substandard
Internal risk grades of non-covered loans
Total loans	95,446	98,806
Noncovered | Secured
Internal risk grades of non-covered loans
Total loans	1,609,136	1,597,112
Noncovered | Secured | Pass
Internal risk grades of non-covered loans
Total loans	1,532,920	1,531,895
Noncovered | Secured | Special Mention
Internal risk grades of non-covered loans
Total loans	19,964	72
Noncovered | Secured | Substandard
Internal risk grades of non-covered loans
Total loans	50,020	56,473
Noncovered | Unsecured
Internal risk grades of non-covered loans
Total loans	126,332	99,341
Noncovered | Unsecured | Pass
Internal risk grades of non-covered loans
Total loans	124,113	97,646
Noncovered | Unsecured | Special Mention
Internal risk grades of non-covered loans
Total loans	996
Noncovered | Unsecured | Substandard
Internal risk grades of non-covered loans
Total loans	1,223	1,695
Noncovered | Secured by Commercial Properties
Internal risk grades of non-covered loans
Total loans	2,189,992	1,955,095
Noncovered | Secured by Commercial Properties | Pass
Internal risk grades of non-covered loans
Total loans	2,125,077	1,888,231
Noncovered | Secured by Commercial Properties | Special Mention
Internal risk grades of non-covered loans
Total loans	4,808	3,693
Noncovered | Secured by Commercial Properties | Substandard
Internal risk grades of non-covered loans
Total loans	40,171	34,661
Noncovered | Secured by Residential Properties
Internal risk grades of non-covered loans
Total loans	754,163	861,672
Noncovered | Secured by Residential Properties | Pass
Internal risk grades of non-covered loans
Total loans	737,712	846,420
Noncovered | Secured by Residential Properties | Special Mention
Internal risk grades of non-covered loans
Total loans	3,263
Noncovered | Secured by Residential Properties | Substandard
Internal risk grades of non-covered loans
Total loans	3,170	4,763
Noncovered | Residential Construction Loans
Internal risk grades of non-covered loans
Total loans	173,479	128,652
Noncovered | Residential Construction Loans | Pass
Internal risk grades of non-covered loans
Total loans	173,479	128,624
Noncovered | Residential Construction Loans | Substandard
Internal risk grades of non-covered loans
Total loans		28
Noncovered | Commercial construction loans and land development
Internal risk grades of non-covered loans
Total loans	768,149	658,198
Noncovered | Commercial construction loans and land development | Pass
Internal risk grades of non-covered loans
Total loans	763,142	653,808
Noncovered | Commercial construction loans and land development | Special Mention
Internal risk grades of non-covered loans
Total loans	2,652
Noncovered | Commercial construction loans and land development | Substandard
Internal risk grades of non-covered loans
Total loans	767	923
Noncovered | Consumer
Internal risk grades of non-covered loans
Total loans	41,958	41,352
Noncovered | Consumer | Pass
Internal risk grades of non-covered loans
Total loans	41,700	40,789
Noncovered | Consumer | Special Mention
Internal risk grades of non-covered loans
Total loans		6
Noncovered | Consumer | Substandard
Internal risk grades of non-covered loans
Total loans	95	263
Noncovered | Broker-dealer
Internal risk grades of non-covered loans
Total loans	485,604	502,077
Noncovered | Broker-dealer | Pass
Internal risk grades of non-covered loans
Total loans	485,604	502,077
Noncovered | PCI loans
Internal risk grades of non-covered loans
Total loans	37,937	51,432
Noncovered | PCI loans | Secured
Internal risk grades of non-covered loans
Total loans	6,232	8,672
Noncovered | PCI loans | Secured by Commercial Properties
Internal risk grades of non-covered loans
Total loans	19,936	28,510
Noncovered | PCI loans | Secured by Residential Properties
Internal risk grades of non-covered loans
Total loans	10,018	10,489
Noncovered | PCI loans | Commercial construction loans and land development
Internal risk grades of non-covered loans
Total loans	1,588	3,467
Noncovered | PCI loans | Consumer
Internal risk grades of non-covered loans
Total loans	$ 163	$ 294