Disclosures About Fair Value of Financial Instruments - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Carrying Amount	$ 262,638	$ 264,593	$ 333,823	$ 371,023
Cash and cash equivalents, Estimated Fair Value	262,638	264,593
Investment securities, available for sale, Carrying Amount	556,165	560,253
Investment securities Fair Value Disclosure	556,165	560,253
Loans held for sale, Carrying Amount	1,969,280	1,797,064
Loans held for sale, Estimated Fair Value	1,969,558	1,797,458
Loans receivable, net of allowance for loan losses, Carrying Amount	5,869,710	5,417,832
Loans receivable, net of allowance for loan losses, Estimated Fair Value	5,825,695	5,353,903
FHLB, Federal Reserve Bank and other restricted stock, Carrying Amount	92,269	90,841
FHLB and Federal Reserve Bank and other restricted stock, Estimated Fair Value	92,269	90,841
Derivatives assets, Carrying Amount	15,324	9,295
Derivatives assets, Fair Value Disclosure	15,324	9,295
Deposits, Carrying Amount	6,478,615	5,909,501
Deposits, Estimated Fair Value	6,486,780	5,911,754
Federal funds purchased, Carrying Amount	80,000	70,000
Federal funds purchased, Estimated Fair Value	80,000	70,000
FHLB advances, Carrying Amount	1,633,700	1,625,300
FHLB advances, Estimated Fair Value	1,635,165	1,625,468
Other borrowings, Carrying Amount	86,624	86,457
Other borrowings, Estimated Fair Value	84,784	93,804
Subordinated debt, Carrying Amount	108,709	108,685
Subordinated debt, Estimated Fair Value	110,000	110,825
Derivatives liabilities, Carrying Amount	22,957	13,932
Derivatives liabilities, Fair Value Disclosure	22,957	13,932
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Estimated Fair Value	262,638	264,593
Investment securities Fair Value Disclosure	17,458	19,212
Loans held for sale, Estimated Fair Value	0	0
Loans receivable, net of allowance for loan losses, Estimated Fair Value	0	0
FHLB and Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
Derivatives assets, Carrying Amount	0	0
Derivatives assets, Fair Value Disclosure	0	0
Deposits, Estimated Fair Value	4,108,287	3,561,905
Federal funds purchased, Estimated Fair Value	80,000	70,000
FHLB advances, Estimated Fair Value	1,323,700	1,365,300
Other borrowings, Estimated Fair Value	59,784	68,867
Subordinated debt, Estimated Fair Value	0	0
Derivatives liabilities, Carrying Amount	0	0
Derivatives liabilities, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Estimated Fair Value	0	0
Investment securities Fair Value Disclosure	538,707	541,041
Loans held for sale, Estimated Fair Value	1,941,602	1,757,807
Loans receivable, net of allowance for loan losses, Estimated Fair Value	0	0
FHLB and Federal Reserve Bank and other restricted stock, Estimated Fair Value	92,269	90,841
Derivatives assets, Carrying Amount	15,251	9,250
Derivatives assets, Fair Value Disclosure	15,251	9,250
Deposits, Estimated Fair Value	2,378,493	2,349,849
Federal funds purchased, Estimated Fair Value	0	0
FHLB advances, Estimated Fair Value	311,465	260,168
Other borrowings, Estimated Fair Value	25,000	24,937
Subordinated debt, Estimated Fair Value	110,000	110,825
Derivatives liabilities, Carrying Amount	22,957	13,932
Derivatives liabilities, Fair Value Disclosure	22,957	13,932
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Estimated Fair Value	0	0
Investment securities Fair Value Disclosure	0	0
Loans held for sale, Estimated Fair Value	27,956	39,651
Loans receivable, net of allowance for loan losses, Estimated Fair Value	5,825,695	5,353,903
FHLB and Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
Derivatives assets, Carrying Amount	73	45
Derivatives assets, Fair Value Disclosure	73	45
Deposits, Estimated Fair Value	0	0
Federal funds purchased, Estimated Fair Value	0	0
FHLB advances, Estimated Fair Value	0	0
Other borrowings, Estimated Fair Value	0	0
Subordinated debt, Estimated Fair Value	0	0
Derivatives liabilities, Carrying Amount	0	0
Derivatives liabilities, Fair Value Disclosure	$ 0	$ 0