Fair Value - Carrying Amounts and Estimated Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Cash and cash equivalents	$ 1,146,691	$ 490,058
Trading securities, at fair value	8,432	4,987
Available for sale debt securities, at fair value	2,138,442	1,886,724
Held to maturity debt securities, carrying amount	195,948	202,903
Loans held for sale, at fair value	188,316	142,801	$ 49,474	$ 40,399
Loans, net, carrying amount	11,868,498	11,943,288
Mortgage servicing assets, carrying amount	1,038	1,332
Mortgage banking derivatives, carrying amount assets	6,436	1,761
Interest rate swap derivatives, carrying amount assets	831,891	273,068
Accrued interest receivable, carrying amount	43,382	40,945
Cash and cash equivalents, fair value	1,146,691	490,058
Held to maturity debt securities, at fair value	205,458	208,852
Loans held for sale (see Note 6)	188,316	142,801	$ 49,474	$ 40,399
Loans, net, fair value	12,008,094	11,925,693
Mortgage servicing assets, at fair value	1,038	1,332
Mortgage banking derivatives, assets fair value	6,436	1,761
Interest rate swap derivatives, assets fair value	831,891	273,068
Accrued interest receivable, fair value	43,382	40,945
Financial liabilities:
Deposits- without stated maturities, carrying amount	11,228,116	10,879,837
Deposits- with stated maturities, carrying amount	2,893,383	2,256,555
Securities sold under agreement to repurchase	81,736	93,141
Federal funds purchased and other borrowings, carrying amount	466,433	540,193
Corporate and subordinated debentures	71,356	71,343
Mortgage banking derivatives, carrying amount liability	6,126	305
Interest rate swap derivatives, carrying amount	842,451	275,033
Accrued interest payable, carrying amount	4,334	3,998
Deposits- without stated maturities, fair value	11,228,116	10,879,837
Deposits- with stated maturities, fair value	2,918,615	2,271,497
Securities sold under agreement to repurchase, fair value	81,736	93,141
Federal funds purchased and other borrowings, fair value	466,433	540,193
Corporate and subordinated debentures	66,669	66,964
Mortgage banking derivatives, liability fair value	6,126	305
Interest rate swap derivatives, fair value	842,451	275,033
Accrued interest payable, fair value	4,334	3,998
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents, fair value	1,146,691	490,058
Financial liabilities:
Deposits- without stated maturities, fair value	11,228,116	10,879,837
Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Trading securities, at fair value	8,432	4,987
Available for sale debt securities, at fair value	2,138,442	1,886,724
Loans held for sale, at fair value	188,316	142,801
Held to maturity debt securities, at fair value	205,458	208,852
Loans held for sale (see Note 6)	188,316	142,801
Mortgage servicing assets, at fair value	1,038	1,332
Mortgage banking derivatives, assets fair value	57	14
Interest rate swap derivatives, assets fair value	831,891	273,068
Accrued interest receivable, fair value	7,594	7,547
Financial liabilities:
Deposits- with stated maturities, fair value	2,918,615	2,271,497
Securities sold under agreement to repurchase, fair value	81,736	93,141
Federal funds purchased and other borrowings, fair value	466,433	540,193
Mortgage banking derivatives, liability fair value	6,032	288
Interest rate swap derivatives, fair value	842,451	275,033
Accrued interest payable, fair value	4,334	3,998
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Loans, net, fair value	12,008,094	11,925,693
Mortgage banking derivatives, assets fair value	6,379	1,747
Accrued interest receivable, fair value	35,788	33,398
Financial liabilities:
Corporate and subordinated debentures	66,669	66,964
Mortgage banking derivatives, liability fair value	$ 94	$ 17