Goodwill and Other Intangible Assets (Detail) - Core Deposit Intangibles - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-lived Intangible Assets [Roll Forward]
Balance at the beginning of the year, gross	$ 47,970	$ 33,775	$ 33,775
Balance at the beginning of the year, accumulated amortization	24,360	21,471	18,193
Balance at the beginning of the year, net	23,610	12,304	15,582
Additions	580	14,195	0
Amortization expense	(3,920)	(2,889)	(3,278)
Balance at the end of the year, gross	48,550	47,970	33,775
Balance at the end of the year, accumulated amortization	28,280	24,360	21,471
Balance at the end of the year, net	$ 20,270	$ 23,610	$ 12,304
Weighted-average remaining life (in years)	7 years 5 months 9 days	8 years	5 years 10 months 8 days
Minimum
Finite-lived Intangible Assets [Roll Forward]
Estimated useful lives (in years)	9 months 6 days	3 months 6 days	2 months 4 days
Maximum
Finite-lived Intangible Assets [Roll Forward]
Estimated useful lives (in years)	10 years	10 years 3 months 6 days	11 years 3 months 6 days