Loans and Leases - Summary of Changes in Accretable Yield for Acquired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Purchased Impaired [Member]
Summary of changes in Accretable Yield for loans acquired at a discount
Balance at beginning of period	$ 154,233	$ 184,618	$ 76,518
Additions			117,251
Interest income	(47,452)	(52,769)	(28,551)
Reclassifications from nonaccretable balance	51,137	22,384	19,400
Balance at end of period	157,918	154,233	184,618
Other Acquired [Member]
Summary of changes in Accretable Yield for loans acquired at a discount
Balance at beginning of period	201,153	296,434	397,379
Interest income	(82,605)	(123,044)	(158,260)
Reclassifications from nonaccretable balance	16,437	22,677	49,930
Other	(1,823)	5,086	7,385
Balance at end of period	$ 133,162	$ 201,153	$ 296,434