Business Segments - Financial Information by Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Interest and dividend income	$ 142,448	$ 119,053
Interest expense	22,286	20,692
Net interest income	120,162	98,361
Provision for credit losses	29,821	2,507
Net interest income after provision for credit losses	90,341	95,854
Non-interest income	28,009	27,773
Non-interest expense	91,333	74,432
Income before provision for income taxes	27,017	49,195
Provision for income taxes	3,621	8,858
Net income	23,396	40,337
Community Banking [Member]
Segment Reporting Information [Line Items]
Interest and dividend income	142,448	119,053
Interest expense	22,286	20,692
Net interest income	120,162	98,361
Provision for credit losses	29,821	2,507
Net interest income after provision for credit losses	90,341	95,854
Non-interest income	21,057	20,658
Non-interest expense	86,918	70,275
Income before provision for income taxes	24,480	46,237
Provision for income taxes	3,088	8,237
Net income	21,392	38,000
Trust and Investment Services [Member]
Segment Reporting Information [Line Items]
Non-interest income	6,952	7,115
Non-interest expense	4,415	4,157
Income before provision for income taxes	2,537	2,958
Provision for income taxes	533	621
Net income	$ 2,004	$ 2,337