Non-Covered Loans and Allowance for Non-Covered Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 item	Dec. 31, 2014
Internal risk grades of non-covered loans
Total	4,834,687	$ 3,920,476
Bank
Internal risk grades of non-covered loans
Number of types of loans	2
Noncovered
Internal risk grades of non-covered loans
Total	4,834,687	3,920,476
Noncovered | Bank
Internal risk grades of non-covered loans
Total	4,834,687	3,920,476
Noncovered | Pass
Internal risk grades of non-covered loans
Total	4,628,624	3,774,559
Noncovered | Special Mention
Internal risk grades of non-covered loans
Total	2,933	1,817
Noncovered | Substandard
Internal risk grades of non-covered loans
Total	88,262	95,191
Noncovered | Secured | Bank
Internal risk grades of non-covered loans
Total	2,112,080	1,648,433
Noncovered | Secured | Pass
Internal risk grades of non-covered loans
Total	2,029,291	1,566,208
Noncovered | Secured | Special Mention
Internal risk grades of non-covered loans
Total	878	1,105
Noncovered | Secured | Substandard
Internal risk grades of non-covered loans
Total	62,008	67,746
Noncovered | Unsecured | Bank
Internal risk grades of non-covered loans
Total	109,647	110,418
Noncovered | Unsecured | Pass
Internal risk grades of non-covered loans
Total	109,555	110,256
Noncovered | Unsecured | Substandard
Internal risk grades of non-covered loans
Total	92	94
Noncovered | Secured by commercial properties | Bank
Internal risk grades of non-covered loans
Total	1,369,298	1,195,912
Noncovered | Secured by commercial properties | Pass
Internal risk grades of non-covered loans
Total	1,284,575	1,151,454
Noncovered | Secured by commercial properties | Special Mention
Internal risk grades of non-covered loans
Total	702	712
Noncovered | Secured by commercial properties | Substandard
Internal risk grades of non-covered loans
Total	21,194	21,405
Noncovered | Secured by residential properties | Bank
Internal risk grades of non-covered loans
Total	697,961	498,923
Noncovered | Secured by residential properties | Pass
Internal risk grades of non-covered loans
Total	672,096	492,549
Noncovered | Secured by residential properties | Special Mention
Internal risk grades of non-covered loans
Total	1,353
Noncovered | Secured by residential properties | Substandard
Internal risk grades of non-covered loans
Total	3,684	4,564
Noncovered | Residential construction loans | Bank
Internal risk grades of non-covered loans
Total	75,131	65,046
Noncovered | Residential construction loans | Pass
Internal risk grades of non-covered loans
Total	74,898	65,046
Noncovered | Commercial construction loans and land development | Bank
Internal risk grades of non-covered loans
Total	418,162	348,597
Noncovered | Commercial construction loans and land development | Pass
Internal risk grades of non-covered loans
Total	407,387	338,078
Noncovered | Commercial construction loans and land development | Substandard
Internal risk grades of non-covered loans
Total	1,247	1,341
Noncovered | Consumer
Internal risk grades of non-covered loans
Total	52,408	53,147
Noncovered | Consumer | Bank
Internal risk grades of non-covered loans
Total	52,408	53,147
Noncovered | Consumer | Pass
Internal risk grades of non-covered loans
Total	50,822	50,968
Noncovered | Consumer | Substandard
Internal risk grades of non-covered loans
Total	37	41
Noncovered | PCI loans
Internal risk grades of non-covered loans
Total	114,868	48,909
Noncovered | PCI loans | Bank
Internal risk grades of non-covered loans
Total	114,868	48,909
Noncovered | PCI loans | Secured | Bank
Internal risk grades of non-covered loans
Total	19,903	13,374
Noncovered | PCI loans | Unsecured | Bank
Internal risk grades of non-covered loans
Total		68
Noncovered | PCI loans | Secured by commercial properties | Bank
Internal risk grades of non-covered loans
Total	62,827	22,341
Noncovered | PCI loans | Secured by residential properties | Bank
Internal risk grades of non-covered loans
Total	20,828	1,810
Noncovered | PCI loans | Residential construction loans | Bank
Internal risk grades of non-covered loans
Total	233
Noncovered | PCI loans | Commercial construction loans and land development | Bank
Internal risk grades of non-covered loans
Total	9,528	9,178
Noncovered | PCI loans | Consumer
Internal risk grades of non-covered loans
Total	1,549	2,138
Noncovered | PCI loans | Consumer | Bank
Internal risk grades of non-covered loans
Total	1,549	$ 2,138