Summary of Significant Accounting Policies (Additional Cash Flow Information) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash paid for interest	$ 24,371	$ 11,886	$ 12,982
Cash paid for income tax	56,359	50,427	57,086
Deferred gain on sale of building and parking garage	0	7,099	0
Unsettled purchases/sales of securities	37,481	0	2,998
Loans foreclosed and transferred to other real estate owned and foreclosed assets	279	0	933
Loans to facilitate the sale of other real estate owned	$ 0	$ 753	$ 20