Goodwill and Other Intangible Assets - Narrative (Detail) - USD ($)		3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 23, 2018	Jan. 12, 2018	Dec. 31, 2017	Jul. 31, 2017
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments		$ 47,267,000
Non-compete agreement				$ 155,900
Title plant assets	$ 6,800,000	6,800,000			$ 6,700,000
Gibraltar Private Bank & Trust Company [Member]
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments	$ 42,500,000
Core deposit intangible assets			$ 18,529,000
Sabadell United
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments		$ 1,400,000
Core deposit intangible assets						$ 66,600,000