Loans and the Allowance for Credit Losses - Summary of Commercial Loans by Risk Grade (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of commercial loans by risk grade
Commercial loans	$ 6,205,762	$ 5,024,132
Commercial Portfolio Segment [Member]
Summary of commercial loans by risk grade
Commercial loans	3,961,629	2,994,259
Commercial Portfolio Segment [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	3,886,886	2,914,553
Commercial Portfolio Segment [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	24,778	26,298
Commercial Portfolio Segment [Member] | Classified - Substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	49,965	53,408
Commercial Portfolio Segment [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	496,539	344,748
Commercial Portfolio Segment [Member] | Commercial Real Estate - Land and Construction [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	489,380	335,989
Commercial Portfolio Segment [Member] | Commercial Real Estate - Land and Construction [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	4,405	5,527
Commercial Portfolio Segment [Member] | Commercial Real Estate - Land and Construction [Member] | Classified - Substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	2,754	3,232
Commercial Portfolio Segment [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	2,376,972	1,911,633
Commercial Portfolio Segment [Member] | Commercial Real Estate - Improved Property [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	2,324,755	1,864,986
Commercial Portfolio Segment [Member] | Commercial Real Estate - Improved Property [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	15,295	10,911
Commercial Portfolio Segment [Member] | Commercial Real Estate - Improved Property [Member] | Classified - Substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	36,922	35,736
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	1,088,118	737,878
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	1,072,751	713,578
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	5,078	9,860
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Classified - Substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	$ 10,289	$ 14,440