Intangible Assets - Summary of Goodwill by Business Segment (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Goodwill [Line Items]
Balance at beginning of period	$ 54,042
Acquisitions	25,691
Balance at end of period	79,733
Metropolitan Banks [Member]
Goodwill [Line Items]
Balance at beginning of period	8,078
Acquisitions	5,689
Balance at end of period	13,767
Community Banks [Member]
Goodwill [Line Items]
Balance at beginning of period	39,876
Acquisitions	20,002
Balance at end of period	59,878
Other Financial Services [Member]
Goodwill [Line Items]
Balance at beginning of period	5,464
Balance at end of period	5,464
Executive, Operations & Support [Member]
Goodwill [Line Items]
Balance at beginning of period	624
Balance at end of period	$ 624