Loans and the Allowance for Credit Losses - Summary of Commercial Loans by Risk Grade (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Summary of commercial loans by risk grade
Commercial loans	$ 10,215,556	$ 7,607,333
Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	7,147,229	5,036,201
Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	118,959	51,710
Classified - substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	91,749	31,244
Classified - doubtful [Member]
Summary of commercial loans by risk grade
Commercial loans	11,770
Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	777,151	528,072
Commercial Real Estate - Land and Construction [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	769,537	523,707
Commercial Real Estate - Land and Construction [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	4,338	2,297
Commercial Real Estate - Land and Construction [Member] | Classified - substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	3,276	2,068
Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	4,947,857	3,325,623
Commercial Real Estate - Improved Property [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	4,807,003	3,267,304
Commercial Real Estate - Improved Property [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	65,612	35,566
Commercial Real Estate - Improved Property [Member] | Classified - substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	75,242	22,753
Commercial and Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	1,644,699	1,265,460
Commercial and Industrial [Member] | Pass [Member]
Summary of commercial loans by risk grade
Commercial loans	1,570,689	1,245,190
Commercial and Industrial [Member] | Criticized [Member]
Summary of commercial loans by risk grade
Commercial loans	49,009	13,847
Commercial and Industrial [Member] | Classified - substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	13,231	6,423
Commercial and Industrial [Member] | Classified - doubtful [Member]
Summary of commercial loans by risk grade
Commercial loans	11,770
Commercial Portfolio Segment [Member]
Summary of commercial loans by risk grade
Commercial loans	$ 7,369,707	$ 5,119,155