Loans and the Allowance for Credit Losses - Recognition of Interest Income on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Receivables [Abstract]
Average impaired loans	$ 40,967	$ 53,801	$ 50,384
Amount of contractual interest income on impaired loans	2,747	3,061	3,260
Amount of interest income recognized on impaired loans	$ 460	$ 1,997	$ 2,049