Non-Covered Loans and Allowance for Non-Covered Loan Losses - Aging (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	$ 5,366,065	$ 5,220,040
Noncovered
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	9,091	18,056
Loans past Due 60-89 Days	1,015	6,822
Loans past Due 90 Days or More	9,339	9,157
Total Past Due Loans	19,445	34,035
Current Loans	5,278,567	5,113,951
Total loans	5,366,065	5,220,040
Accruing Loans Past Due 90 Days or More	1,229	12
Noncovered | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	68,053	72,054
Noncovered | Secured
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	2,347	14,869
Loans past Due 60-89 Days	915	3,960
Loans past Due 90 Days or More	7,819	8,414
Total Past Due Loans	11,081	27,243
Current Loans	1,496,644	1,406,537
Total loans	1,520,842	1,447,130
Accruing Loans Past Due 90 Days or More	46	12
Noncovered | Secured | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	13,117	13,350
Noncovered | Unsecured
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	637	18
Loans past Due 60-89 Days	51	1
Total Past Due Loans	688	19
Current Loans	98,037	105,656
Total loans	98,725	105,675
Noncovered | Secured by commercial properties
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	1,153	1,008
Loans past Due 60-89 Days		964
Loans past Due 90 Days or More	1,519	293
Total Past Due Loans	2,672	2,265
Current Loans	1,684,700	1,528,084
Total loans	1,725,988	1,571,477
Accruing Loans Past Due 90 Days or More	1,183
Noncovered | Secured by commercial properties | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	38,616	41,128
Noncovered | Secured by residential properties
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	4,483	726
Loans past Due 60-89 Days	22	35
Loans past Due 90 Days or More		336
Total Past Due Loans	4,505	1,097
Current Loans	794,115	729,018
Total loans	810,314	741,762
Noncovered | Secured by residential properties | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	11,694	11,647
Noncovered | Residential construction loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	28	343
Total Past Due Loans	28	343
Current Loans	97,276	103,819
Total loans	97,304	104,383
Noncovered | Residential construction loans | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans		221
Noncovered | Commercial construction loans and land development
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days		733
Loans past Due 60-89 Days		1,845
Loans past Due 90 Days or More		114
Total Past Due Loans		2,692
Current Loans	599,956	593,352
Total loans	604,054	600,973
Noncovered | Commercial construction loans and land development | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	4,098	4,929
Noncovered | Consumer
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Loans past Due 30-59 Days	443	359
Loans past Due 60-89 Days	27	17
Loans past Due 90 Days or More	1
Total Past Due Loans	471	376
Current Loans	43,852	44,517
Total loans	44,851	45,672
Noncovered | Consumer | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	528	779
Noncovered | Broker-dealer
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Current Loans	463,987	602,968
Total loans	463,987	602,968
Noncovered | Prime Lending
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Accruing Loans Past Due 90 Days or More	50,700
Noncovered | Prime Lending | U.S. Government Agencies
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Accruing Loans Past Due 90 Days or More		50,800
Unpaid principal balance loans past due 90 days or more	$ 51,200	$ 51,100