Loans - Average Recorded Investment In Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 83,747	$ 46,458	$ 104,198	$ 49,091
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	26,921	25,487	25,365	28,457
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	47,003	6,883	57,309	3,760
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	8,904	13,003	20,444	14,658
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	326	249	548	1,507
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	545	836	508	709
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 48	$ 0	$ 24	$ 0