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, 2019
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 147,104	$ 147,210
Interest income	(9,564)	(37,278)
Reclassifications from nonaccretable balance	9,079	36,687
Balance at end of period	146,619	146,619
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	90,911	96,907
Interest income	(9,238)	(28,621)
Reclassifications from nonaccretable balance	3,990	12,312
Other	41	5,106
Balance at end of period	$ 85,704	$ 85,704