Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Goodwill [Line Items]
Beginning balance	$ 584,634	$ 530,845
Goodwill acquired during the period		57,059
Ending balance	$ 584,634	587,904
Banking [Member]
Goodwill [Line Items]
Beginning balance	543,671	490,972
Goodwill acquired during the period		55,969
Ending balance	543,671	546,941
Insurance [Member]
Goodwill [Line Items]
Beginning balance	40,963	39,873
Goodwill acquired during the period		1,090
Ending balance	$ 40,963	$ 40,963