Condensed Financial Information - Parent Company Only - Schedule of Condensed Cash Flow Statement (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 6,918	$ 58	$ 5,240	$ 7,289	$ 7,158	$ 7,528	$ 6,466	$ 6,116	$ 19,505	$ 27,268	$ 22,231
Adjustments to reconcile net income to net cash provided by operating activities:
Net gain on sales of investment securities									(518)	(1,265)	(635)
Bank owned life insurance income									(2,931)	(1,295)	(1,628)
Depreciation of premises and equipment									4,089	3,757	3,243
Stock-based compensation									2,084	1,421	1,141
Contributions to pension and other postretirement benefit plans									(2,261)	(2,271)	(254)
Decrease (increase) in other assets									1,956	3,055	(3,237)
Increase (decrease) in accrued interest payable and other liabilities									2,160	1,442	(587)
Net cash provided by operating activities									33,306	39,343	29,723
Cash flows from investing activities:
Outlays for business acquisitions									(94,835)	(2,967)	(9,260)
Net cash used in investing activities									(294,557)	(190,042)	(36,295)
Cash flows from financing activities:
Proceeds from issuance of subordinated notes									44,515	49,267	0
Purchases of treasury stock									(8,359)	(13,342)	(4,605)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs									2,472	2,434	2,462
Cash dividends paid									(17,024)	(15,011)	(12,996)
Net cash provided by financing activities									277,652	151,060	5,921
Net (decrease) increase in cash and due from financial institutions									16,401	361	(651)
Cash and due from banks at beginning of year				32,356				31,995	32,356	31,995	32,646
Cash and due from banks at end of period	48,757				32,356				48,757	32,356	31,995
Cash paid during the year for:
Interest									13,982	8,099	4,118
Income tax, net of refunds received									8,053	2,142	5,899
Parent Company [Member]
Cash flows from operating activities:
Net income									19,505	27,268	22,231
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net loss (income) of subsidiaries									67,056	(3,137)	(8,913)
Net gain on sales of investment securities									(23)	(285)	(306)
Bank owned life insurance income									(182)	(5)	(238)
Depreciation of premises and equipment									339	275	364
Stock-based compensation									2,084	1,421	1,141
Contributions to pension and other postretirement benefit plans									(2,261)	(2,271)	(254)
Decrease (increase) in other assets									1,098	(4,268)	714
Increase (decrease) in accrued interest payable and other liabilities									213	2,027	(639)
Net cash provided by operating activities									87,829	21,025	14,100
Cash flows from investing activities:
Investments in subsidiaries									(40,000)	(30,000)	0
Proceeds from sales of securities									38	708	1,131
Outlays for business acquisitions									(87,683)	0	0
Other, net									(1,619)	(1,640)	(281)
Net cash used in investing activities									(129,264)	(30,932)	850
Cash flows from financing activities:
Net decrease in short-term borrowings									(253)	0	0
Proceeds from issuance of subordinated notes									44,515	49,267	0
Purchases of treasury stock									(8,359)	(13,342)	(4,605)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs									2,472	2,434	2,462
Proceeds from exercise of stock options, including excess tax benefits									4,968	534	310
Cash dividends paid									(17,024)	(15,010)	(12,996)
Net cash provided by financing activities									26,319	23,883	(14,829)
Net (decrease) increase in cash and due from financial institutions									(15,116)	13,976	121
Cash and due from banks at beginning of year				$ 17,096				$ 3,120	17,096	3,120	2,999
Cash and due from banks at end of period	$ 1,980				$ 17,096				1,980	17,096	3,120
Cash paid during the year for:
Interest									3,956	1,275	2
Income tax, net of refunds received									$ 6,675	$ 1,770	$ 5,300