Fair Value Accounting - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities	$ 92,079		$ 0
Impaired Financing Receivable, Recorded Investment	99,209		128,874
Financial assets
Securities available for sale	2,609,380		1,982,523
Securities measured at fair value	1,053		1,481
Derivative Asset	2,351		3,569		$ 7
Loans, net	13,064,823		10,993,786
Financial liabilities
Deposits	14,549,863		12,030,624
Customer repurchases	41,728		38,155
FHLB and FRB advances	80,000		150,000
Junior subordinated debt	50,410		46,928
Derivative Liability	63,880		64,785		$ 57,820
Other Repossessed Assets	47,800		43,900
Fair Value, Measurements, Nonrecurring [Member]
Financial liabilities
Other Repossessed Assets	47,815
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
Financial liabilities
Other Repossessed Assets	0		0
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
Financial liabilities
Other Repossessed Assets	0		0
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired Financing Receivable, Recorded Investment	67,408		86,383
Financial liabilities
Other Repossessed Assets	47,815		43,942
Fair Value, Measurements, Nonrecurring [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities	92,079
Financial assets
Loans, net	13,083,732		11,017,595
Financial liabilities
Deposits	14,549,863		12,030,624
Junior subordinated debt	367,937		210,238
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities	91,966
Financial assets
Loans, net	12,803,744		10,853,209
Financial liabilities
Deposits	14,553,931		12,034,199
Junior subordinated debt	375,626		207,437
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities	0
Financial assets
Loans, net	0		0
Financial liabilities
Deposits	0		0
Junior subordinated debt	0		0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities	91,966
Financial assets
Loans, net	12,736,336		10,766,826
Financial liabilities
Deposits	14,553,931		12,034,199
Junior subordinated debt	0		0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities	0
Financial assets
Loans, net	67,408		86,383
Financial liabilities
Deposits	0		0
Junior subordinated debt	375,626		207,437
Fair Value, Measurements, Recurring [Member]
Financial assets
Securities available for sale	2,609,380		1,982,523
Derivative Asset	4,220	[1]	3,569	[2]
Financial liabilities
Derivative Liability	65,749	[1]	64,785	[2]
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial assets
Securities available for sale	151,775		148,914
Derivative Asset	0	[1]	0	[2]
Financial liabilities
Junior subordinated debt	0		0
Derivative Liability	0	[1]	0	[2]
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial assets
Securities available for sale	2,457,605		1,823,549
Derivative Asset	4,220	[1]	3,569	[2]
Financial liabilities
Junior subordinated debt	0		0
Derivative Liability	65,749	[1]	64,785	[2]
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial assets
Securities available for sale	0		10,060
Derivative Asset	0	[1]	0	[2]
Financial liabilities
Junior subordinated debt	50,410		46,928
Derivative Liability	0	[1]	0	[2]
Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Financial assets
Securities available for sale	2,609,380		1,982,523
Securities measured at fair value	1,053		1,481
Derivative Asset	4,220		3,569
Accrued Investment Income Receivable	70,320		54,445
Financial liabilities
Customer repurchases	41,728		38,155
Federal Home Loan Bank Borrowings, Fair Value Disclosure	80,000		150,000
Derivative Liability	65,749		64,785
Interest Payable, Current	15,354		13,626
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Financial assets
Securities available for sale	2,609,380		1,982,523
Securities measured at fair value	1,053		1,481
Derivative Asset	4,220		3,569
Accrued Investment Income Receivable	70,320		54,445
Financial liabilities
Customer repurchases	41,728		38,155
Federal Home Loan Bank Borrowings, Fair Value Disclosure	80,000		150,000
Derivative Liability	65,749		64,785
Interest Payable, Current	15,354		13,626
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 1 [Member]
Financial assets
Securities available for sale	151,775		148,914
Securities measured at fair value	0		0
Derivative Asset	0		0
Accrued Investment Income Receivable	0		0
Financial liabilities
Customer repurchases	0		0
Federal Home Loan Bank Borrowings, Fair Value Disclosure	0		0
Derivative Liability	0		0
Interest Payable, Current	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member]
Financial assets
Securities available for sale	2,457,605		1,823,549
Securities measured at fair value	1,053		1,481
Derivative Asset	4,220		3,569
Accrued Investment Income Receivable	70,320		54,445
Financial liabilities
Customer repurchases	41,728		38,155
Federal Home Loan Bank Borrowings, Fair Value Disclosure	80,000		150,000
Derivative Liability	65,749		64,785
Interest Payable, Current	15,354		13,626
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 3 [Member]
Financial assets
Securities available for sale	0		10,060
Securities measured at fair value	0		0
Derivative Asset	0		0
Accrued Investment Income Receivable	0		0
Financial liabilities
Customer repurchases	0		0
Federal Home Loan Bank Borrowings, Fair Value Disclosure	0		0
Derivative Liability	0		0
Interest Payable, Current	$ 0		$ 0
Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Discounted cash flow method		Discounted cash flow method
Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Collateral method		Collateral method
Collateral Method [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Collateral method		Collateral method
Third Party Appraisal [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Third party appraisal		Third party appraisal
Fair Value Measurements, Significant Assumptions	Costs to sell		Costs to sell
Third Party Appraisal [Member] | Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Third party appraisal		Third party appraisal
Fair Value Measurements, Significant Assumptions	Costs to sell		Costs to sell
Discount Rate [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Discount rate		Discount rate
Fair Value Measurements, Significant Assumptions	Contractual loan rate		Contractual loan rate
Scheduled Cash Collections [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Scheduled cash collections		Scheduled cash collections
Fair Value Measurements, Significant Assumptions	Loss given default		Loss given default
Proceeds from Non-Real Estate Collateral [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique	Proceeds from non-real estate collateral		Proceeds from non-real estate collateral
Fair Value Measurements, Significant Assumptions	Loss given default		Loss given default

[1] Derivative assets and liabilities relate to interest rate swaps, see "Note 13. Derivatives and Hedging Activities." In addition, the carrying value of loans includes a net positive value of $48,161 and the net carrying value of subordinated debt includes a net negative value of $12,325 as of December 31, 2016, which relates to the effective portion of the hedges put in place to mitigate against fluctuations in interest rates.

[2] Derivative assets and liabilities relate to interest rate swaps, see "Note 13. Derivatives and Hedging Activities." In addition, the carrying value of loans includes a net positive value of $64,184 and the net carrying value of subordinated debt includes a net negative value of $3,569 as of December 31, 2015, which relates to the effective portion of the hedges put in place to mitigate against fluctuations in interest rates.