Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill not subject to amortization	$ 710,252	$ 709,794
Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	60,577	60,577
Accumulated Amortization	(41,027)	(39,317)
Net Carrying Amount	$ 19,550	$ 21,260