Amount, before tax, of (gain) loss recognized for the (reversal of write-down) write-down to fair value, less cost to sell, of a disposal group. Excludes discontinued operations.

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LOAN PORTFOLIO - Loan Portfolio Held for Investment (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	$ 90,319	$ 0	$ 10,332
Loans and Leases Receivable, Gross	8,858,123	8,850,476	8,886,873
Commercial Mortgage Backed Securities [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	796,800	833,500
Commercial And Industrial Sector [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	2,148,111	2,083,253
Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	79,429	111,397	$ 124,951
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,522,662	$ 1,614,972
Nonperforming Financial Instruments [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	74,400
Fair value write-downs	22,200
Nonperforming Financial Instruments [Member] \| Commercial And Industrial Sector [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	1,800
Fair value write-downs	1,700
Nonperforming Financial Instruments [Member] \| Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	33,000
Fair value write-downs	6,700
Nonperforming Financial Instruments [Member] \| Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	39,600
Fair value write-downs	13,800
Nonperforming Financial Instruments [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] \| Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	30,000
Nonperforming Financial Instruments [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] \| Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment transferred to held for sale	$ 27,200