Significant Accounting Policies - Additional Cash Flow Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Cash paid for interest	$ 15,611	$ 8,731
Cash paid for income taxes	41,969	39,160
Unsettled purchases of securities	41,763	54,342
Loans foreclosed and transferred to other real estate owned and foreclosed assets	$ 257	$ 422