Goodwill and Other Intangible Assets - Schedule of Definite-Lived Intangible Assets at Carrying Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets
Gross carrying amount	$ 75,411	$ 75,654
Accumulated amortization	(51,159)	(45,134)
Net carrying amount	24,252	30,520
Core Deposit Intangibles
Acquired Finite-Lived Intangible Assets
Gross carrying amount	74,001	74,001
Accumulated amortization	(50,128)	(43,957)
Net carrying amount	23,873	30,044
Customer Relationships Intangible Asset
Acquired Finite-Lived Intangible Assets
Gross carrying amount	1,348	1,348
Accumulated amortization	(1,013)	(984)
Net carrying amount	335	364
Non-Compete Agreements
Acquired Finite-Lived Intangible Assets
Gross carrying amount	62	100
Accumulated amortization	(18)	(79)
Net carrying amount	44	21
Other Intangible Assets
Acquired Finite-Lived Intangible Assets
Gross carrying amount	0	205
Accumulated amortization	0	(114)
Net carrying amount	$ 0	$ 91