Disclosures About Fair Value of Financial Instruments - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Carrying Amount	$ 302,796	$ 264,593	$ 391,589	$ 371,023
Cash and cash equivalents, Estimated Fair Value	302,796	264,593
Investment securities, available for sale, Carrying Amount	547,935	560,253
Investment securities, Estimated Fair Value	547,935	560,253
Loans held for sale, Carrying Amount	2,301,821	1,797,064
Loans held for sale, Estimated Fair Value	2,301,821	1,797,458
Loans receivable, net of allowance for loan losses, Carrying Amount	6,076,479	5,417,832
Loans receivable, net of allowance for loan losses, Estimated Fair Value	6,105,391	5,353,903
FHLB, Federal Reserve Bank and other restricted stock, Carrying Amount	111,418	90,841
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	111,418	90,841
Derivative assets, Carrying Amount	19,492	9,295
Derivative assets, Estimated Fair Value	19,492	9,295
Deposits, Carrying Amount	6,751,259	5,909,501
Deposits, Estimated Fair Value	6,762,470	5,911,754
Federal funds purchased, Carrying Amount	61,000	70,000
Federal funds purchased, Estimated Fair Value	61,000	70,000
FHLB advances, Carrying Amount	1,906,900	1,625,300
FHLB advances, Estimated Fair Value	1,908,421	1,625,468
Other borrowings, Carrying Amount	86,790	86,457
Other borrowings, Estimated Fair Value	88,579	93,804
Subordinated debt, Carrying Amount	108,734	108,685
Subordinated debt, Estimated Fair Value	110,000	110,825
Derivative liabilities, Carrying Amount	27,624	13,932
Derivative liabilities, Estimated Fair Value	27,624	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	302,796	264,593
Investment securities, Estimated Fair Value	16,693	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, Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
Derivative assets, Carrying Amount	0	0
Derivative assets, Estimated Fair Value	0	0
Deposits, Estimated Fair Value	4,020,501	3,561,905
Federal funds purchased, Estimated Fair Value	61,000	70,000
FHLB advances, Estimated Fair Value	1,646,900	1,365,300
Other borrowings, Estimated Fair Value	63,579	68,867
Subordinated debt, Estimated Fair Value	0	0
Derivative liabilities, Carrying Amount	0	0
Derivative liabilities, Estimated Fair Value	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, Estimated Fair Value	531,242	541,041
Loans held for sale, Estimated Fair Value	2,274,294	1,757,807
Loans receivable, net of allowance for loan losses, Estimated Fair Value	0	0
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	111,418	90,841
Derivative assets, Carrying Amount	19,335	9,250
Derivative assets, Estimated Fair Value	19,335	9,250
Deposits, Estimated Fair Value	2,741,969	2,349,849
Federal funds purchased, Estimated Fair Value	0	0
FHLB advances, Estimated Fair Value	261,521	260,168
Other borrowings, Estimated Fair Value	25,000	24,937
Subordinated debt, Estimated Fair Value	110,000	110,825
Derivative liabilities, Carrying Amount	27,624	13,932
Derivative liabilities, Estimated Fair Value	27,624	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, Estimated Fair Value	0	0
Loans held for sale, Estimated Fair Value	27,527	39,651
Loans receivable, net of allowance for loan losses, Estimated Fair Value	6,105,391	5,353,903
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
Derivative assets, Carrying Amount	157	45
Derivative assets, Estimated Fair Value	157	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
Derivative liabilities, Carrying Amount	0	0
Derivative liabilities, Estimated Fair Value	$ 0	$ 0