Loans - Non-Accrual Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 177,455	$ 83,467
Commercial Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	26,922	25,111
Commercial and industrial, Energy [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	114,124	21,180
Commercial real estate, Buildings, land and other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	33,449	34,519
Construction Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	970	569
Consumer Real Estate [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	1,770	1,862
Consumer and Other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 220	$ 226