Significant Accounting Policies - Additional Cash Flow Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Cash paid for interest	$ 31,962	$ 6,666
Cash paid for income taxes	3,888	22,801
Unsettled purchases of securities	2,186	80,586
Loans foreclosed and transferred to other real estate owned and foreclosed assets	$ 2,656	$ 0