Assets Acquired in FDIC-Assisted Acquisitions - Changes in FDIC Shared-Loss Receivable (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Business Combinations [Abstract]
Beginning balance	$ 31,351	$ 65,441	$ 65,441
Payments received from FDIC	(12,539)	(10,576)	(22,494)
Accretion (amortization)	(5,393)	(11,390)	(18,449)
Changes in clawback liability	(1,057)	(228)	(1,222)
Charge-offs on covered loans	1,955	2,372	3,372
Write downs of covered other real estate	2,206	2,090	4,771
Reimbursable expenses on covered assets	1,866	2,248	1,078
Other activity, net	(3,432)	(777)	(1,146)
Ending balance	$ 14,957	$ 49,180	$ 31,351