Disclosures about Fair Value of Financial Instruments - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Carrying Amount	$ 391,589	$ 371,023	$ 265,534	$ 233,068
Cash and cash equivalents, Estimated Fair Value	391,589	371,023
Investment securities, available for sale, Carrying Amount	373,953	416,685
Investment securities, available for sale, Estimated Fair Value	373,953	416,685
Loans held for sale, Carrying Amount	2,030,348	1,435,459
Loans held for sale, Estimated Fair Value	2,030,954	1,436,460
Loans receivable, net of allowance for loan losses, Carrying Amount	4,487,334	4,281,241
Loans receivable, net of allowance for loan losses, Estimated Fair Value	4,489,039	4,285,537
FHLB, Federal Reserve Bank and other restricted stock, Carrying Amount	78,148	82,002
FHLB and Federal Reserve Bank and other restricted stock, Estimated Fair Value	78,148	82,002
FDIC loss sharing receivable, Carrying Amount	0	2,320
FDIC loss sharing receivable, Estimated Fair Value		2,320
Derivatives assets, Carrying Amount	6,768	7,552
Derivatives assets, Estimated Fair Value	6,768	7,552
Deposits, Carrying Amount	5,477,157	4,532,538
Deposits, Estimated Fair Value	5,488,758	4,540,507
FHLB advances, Carrying Amount	1,388,000	1,618,000
FHLB advances, Estimated Fair Value	1,390,872	1,619,858
Other borrowings, Carrying Amount	88,250	88,250
Other borrowings, Estimated Fair Value	93,560	92,069
Subordinated debt, Carrying Amount	110,000	110,000
Subordinated debt, Estimated Fair Value	113,025	111,925
FDIC clawback liability, net of FDIC receivable, Estimated Fair Value	1,455
Derivatives liabilities, Carrying Amount	10,234	9,716
Derivatives liabilities, Estimated Fair Value	10,234	9,716
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	391,589	371,023
Investment securities, available for sale, Carrying Amount	20,274	24,270
Investment securities, available for sale, Estimated Fair Value	20,274	24,270
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
FDIC loss sharing receivable, Estimated Fair Value		0
Derivatives assets, Carrying Amount	0	0
Derivatives assets, Estimated Fair Value	0	0
Deposits, Estimated Fair Value	3,215,694	2,820,875
FHLB advances, Estimated Fair Value	1,018,153	1,298,000
Other borrowings, Estimated Fair Value	68,310	66,944
Subordinated debt, Estimated Fair Value	0	0
FDIC clawback liability, net of FDIC receivable, Estimated Fair Value	0
Derivatives liabilities, Carrying Amount	0	0
Derivatives 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, available for sale, Carrying Amount	353,679	392,415
Investment securities, available for sale, Estimated Fair Value	353,679	392,415
Loans held for sale, Estimated Fair Value	1,949,572	1,335,668
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	78,148	82,002
FDIC loss sharing receivable, Estimated Fair Value		0
Derivatives assets, Carrying Amount	6,697	7,509
Derivatives assets, Estimated Fair Value	6,697	7,509
Deposits, Estimated Fair Value	2,273,064	1,719,632
FHLB advances, Estimated Fair Value	372,719	321,858
Other borrowings, Estimated Fair Value	25,250	25,125
Subordinated debt, Estimated Fair Value	113,025	111,925
FDIC clawback liability, net of FDIC receivable, Estimated Fair Value	0
Derivatives liabilities, Carrying Amount	10,234	9,716
Derivatives liabilities, Estimated Fair Value	10,234	9,716
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, available for sale, Carrying Amount	0	0
Investment securities, available for sale, Estimated Fair Value	0	0
Loans held for sale, Estimated Fair Value	81,382	100,792
Loans receivable, net of allowance for loan losses, Estimated Fair Value	4,489,039	4,285,537
FHLB and Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
FDIC loss sharing receivable, Estimated Fair Value		2,320
Derivatives assets, Carrying Amount	71	43
Derivatives assets, Estimated Fair Value	71	43
Deposits, 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
FDIC clawback liability, net of FDIC receivable, Estimated Fair Value	1,455
Derivatives liabilities, Carrying Amount	0	0
Derivatives liabilities, Estimated Fair Value	$ 0	$ 0