Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014
Goodwill [Line Items]
Beginning balance	$ 530,845	$ 352,729	$ 352,729
Goodwill acquired during the period	57,059
Ending balance	587,904	352,729	352,729
Banking [Member]
Goodwill [Line Items]
Beginning balance	490,972	312,856	312,856
Goodwill acquired during the period	55,969
Ending balance	546,941	312,856	312,856
Insurance [Member]
Goodwill [Line Items]
Beginning balance	39,873	39,873	39,873
Goodwill acquired during the period	1,090
Ending balance	40,963	39,873	39,873
Other [Member]
Goodwill [Line Items]
Beginning balance
Ending balance