Fair Value Measurements (Details 8) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 245,998	$ 233,215
Interest-earning deposits in financial institutions	205,567	165,222
Securities available-for-sale, Carrying Amount		3,774,431
Securities available-for-sale, at fair value	3,857,788	3,774,431
Investment in FHLB stock, Carrying Amount	26,271	20,790
Investment in FHLB stock, Fair Value	26,271	20,790
Loans held for sale, at lower of cost or fair value	0	481,100
Loans Held-for-sale, Fair Value Disclosure		483,563
Loans and leases, net	16,753,053	16,833,287
Loans and leases held for investment, net	16,438,905
Warrants and Rights Outstanding		5,161
Equity warrants		5,161
Other derivative assets, Carrying Amount	2,814	1,873
Fair Value, Estimate Not Practicable, Equity Method Investments	4,569
Demand, interest checking, money market, and savings deposits	15,586,238	15,937,012
Interest-bearing Domestic Deposit, Brokered	607,388	863,202
Time deposits	1,735,566	2,065,322
Time deposits	1,724,232	2,055,104
Borrowings	1,187,226	467,342
Borrowings	1,187,168	467,342
Subordinated debentures	451,878	462,437
Subordinated debentures	435,641	444,383
Derivative Liability	362	1,379
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	245,998	233,215
Interest-earning deposits in financial institutions	205,567	165,222
Securities available-for-sale, at fair value		5,922
Investment in FHLB stock, Fair Value	0	0
Demand, interest checking, money market, and savings deposits	0	0
Interest-bearing Domestic Deposit, Brokered	0	0
Time deposits	0	0
Borrowings	1,186,000	467,000
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
Securities available-for-sale, at fair value		3,703,526
Investment in FHLB stock, Fair Value	26,271	20,790
Demand, interest checking, money market, and savings deposits	15,586,238	15,937,012
Interest-bearing Domestic Deposit, Brokered	607,388	863,202
Time deposits	1,724,232	2,055,104
Borrowings	1,168	342
Subordinated debentures	435,641	444,383
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
Securities available-for-sale, at fair value		64,983
Investment in FHLB stock, Fair Value	0	0
Loans and leases held for investment, net	16,423,043
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]
Securities available-for-sale, at fair value	3,857,788	3,774,431
Equity warrants	5,168	5,161
Other derivative assets, Fair Value	2,814	1,873
Derivative liabilities	362	1,379
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, at fair value	262,341	5,922
Equity warrants	0	0
Other derivative assets, Fair Value	0	0
Fair Value, Estimate Not Practicable, Equity Method Investments	4,569
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, at fair value	3,548,863	3,703,526
Equity warrants	0	0
Other derivative assets, Fair Value	2,814	1,873
Fair Value, Estimate Not Practicable, Equity Method Investments	0
Derivative liabilities	362	1,379
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, at fair value	46,584	64,983
Equity warrants	5,168	5,161
Other derivative assets, Fair Value	0	0
Fair Value, Estimate Not Practicable, Equity Method Investments	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		483,563
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, net		16,833,287
Loans and leases held for investment, net		17,023,098
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	$ 15,862	5,143
NonPCI and PCI Loans | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net		$ 17,017,955