Fair Value Measurements (Details 8) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 224,758	$ 175,830
Interest-earning deposits in financial institutions	332,124	209,937
Securities available-for-sale, Carrying Amount	3,994,708	4,009,431
Investment in FHLB stock, Carrying Amount	29,430	32,103
Investment in FHLB stock, Fair Value	29,430	32,103
Loans held for sale	25,124	0
Loans Held-for-sale, Fair Value Disclosure	25,124
Loans and leases, net	18,171,416	17,825,241
Loans and leases held for investment, net	17,719,820
Warrants and Rights Outstanding		4,793
Other derivative assets, Carrying Amount	2,493	3,292
Fair Value, Estimate Not Practicable, Equity Method Investments	3,848	4,891
Demand, interest checking, money market, and savings deposits	16,127,638	16,346,671
Interest-bearing Domestic Deposit, Brokered	454,277	518,192
Time deposits	2,704,012	2,005,638
Time deposits	2,697,119	2,017,137
Borrowings	1,481,087	1,371,114
Borrowings	1,481,085	1,371,114
Subordinated debentures	454,458	453,846
Subordinated debentures	438,207	435,251
Derivative Liability	633	142
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	224,758	175,830
Interest-earning deposits in financial institutions	332,124	209,937
Investment in FHLB stock, Fair Value	0	0
Loans Held-for-sale, Fair Value Disclosure	0
Demand, interest checking, money market, and savings deposits	0	0
Interest-bearing Domestic Deposit, Brokered	0	0
Time deposits	0	0
Borrowings	1,471,000	1,371,000
Subordinated debentures	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	0	0
Interest-earning deposits in financial institutions	0	0
Investment in FHLB stock, Fair Value	29,430	32,103
Loans Held-for-sale, Fair Value Disclosure	25,124
Demand, interest checking, money market, and savings deposits	16,127,638	16,346,671
Interest-bearing Domestic Deposit, Brokered	454,277	518,192
Time deposits	2,697,119	2,017,137
Borrowings	10,085	114
Subordinated debentures	438,207	435,251
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	0	0
Interest-earning deposits in financial institutions	0	0
Investment in FHLB stock, Fair Value	0	0
Loans Held-for-sale, Fair Value Disclosure	0
Loans and leases held for investment, net	17,711,934
Equity warrants		4,793
Demand, interest checking, money market, and savings deposits	0	0
Interest-bearing Domestic Deposit, Brokered	0	0
Time deposits	0	0
Borrowings	0	0
Subordinated debentures	0	0
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity warrants	4,438	4,793
Other derivative assets, Fair Value	2,493	3,292
Derivative liabilities	633	142
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Carrying Amount	290,717	403,405
Equity warrants	0	0
Other derivative assets, Fair Value	0	0
Fair Value, Estimate Not Practicable, Equity Method Investments	3,848	4,891
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Carrying Amount	3,661,502	3,558,793
Equity warrants	0	0
Other derivative assets, Fair Value	2,493	3,292
Fair Value, Estimate Not Practicable, Equity Method Investments	0	0
Derivative liabilities	633	142
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Carrying Amount	42,489	47,233
Equity warrants	4,438	4,793
Other derivative assets, Fair Value	0	0
Fair Value, Estimate Not Practicable, Equity Method Investments	0	0
Derivative liabilities	0	0
Non Purchased Credit Impaired Loans and Leases | Fair Value, Measurements, Nonrecurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Held-for-sale, Fair Value Disclosure	0
Non Purchased Credit Impaired Loans and Leases | Fair Value, Measurements, Nonrecurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Held-for-sale, Fair Value Disclosure	25,124
Non Purchased Credit Impaired Loans and Leases | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Held-for-sale, Fair Value Disclosure	0
NonPCI and PCI Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net		17,013,860
NonPCI and PCI Loans | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net	0	0
NonPCI and PCI Loans | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net	$ 7,886	1,800
NonPCI and PCI Loans | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net		$ 17,012,060