Loans and Leases and the Allowance for Credit Losses - Summary of Changes in Accretable Yield for Acquired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 147,104	$ 149,388	$ 147,210	$ 157,918
Interest income	(9,564)	(8,105)	(37,278)	(25,893)
Reclassifications from nonaccretable balance	9,079	8,445	36,687	17,703
Balance at end of period	146,619	149,728	146,619	149,728
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	90,911	117,715	96,907	133,162
Interest income	(9,238)	(18,001)	(28,621)	(48,507)
Reclassifications from nonaccretable balance	3,990	25	12,312	11,230
Other	41	2,001	5,106	5,855
Balance at end of period	$ 85,704	$ 101,740	$ 85,704	$ 101,740