Loans - Summary of Changes in Accretable Yields of Acquired Loans (Detail) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period		$ 287,651	$ 354,892
Acquisition		4,592	9,778
Transfers from non-accretable difference to accretable yield		7,199	17,824
Accretion		(60,305)	(79,356)
Changes in expected cash flows not affecting nonaccretable differences	[1]	(1,511)	(26,250)
Balance at end of period		237,626	276,888
Acquired Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period		74,249	78,349
Acquisition		4,592	8,242
Transfers from non-accretable difference to accretable yield		70	3,952
Accretion		(9,774)	(12,766)
Changes in expected cash flows not affecting nonaccretable differences	[1]	1,209	(6,873)
Balance at end of period		70,346	70,904
Acquired Performing Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period		213,402	276,543
Acquisition		0	1,536
Transfers from non-accretable difference to accretable yield		7,129	13,872
Accretion		(50,531)	(66,590)
Changes in expected cash flows not affecting nonaccretable differences	[1]	(2,720)	(19,377)
Balance at end of period		$ 167,280	$ 205,984

[1] Includes changes in cash flows expected to be collected due to the impact of changes in actual or expected timing of liquidation events, modifications, changes in interest rates and changes in prepayment assumptions.