Intangible Assets - Summary of Goodwill by Business Segment (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Line Items]
Balance at beginning of period	$ 54,042
Acquisitions	25,754
Balance at end of period	79,796
Metropolitan Banks [Member]
Goodwill [Line Items]
Balance at beginning of period	8,078
Acquisitions	1,127
Balance at end of period	9,205
Community Banks [Member]
Goodwill [Line Items]
Balance at beginning of period	40,050
Acquisitions	24,627
Balance at end of period	64,677
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	450
Balance at end of period	$ 450