Parent Company Financial Statements - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net income	$ 4,502	$ 7,556	$ 8,189	$ 1,538	$ 5,025	$ 5,153	$ 5,330	$ 3,320	$ 21,785	$ 18,828	$ 16,282
Adjustments to reconcile net income to net cash provided by operating activities:
Increase (decrease) in other liabilities									3,476	4,059	(1,529)
Net cash from operating activities									49,718	8,510	13,750
Cash Flows from Investing Activities
Net cash from investing activities									(148,124)	(177,145)	(148,300)
Cash Flows from Financing Activities
Purchase of treasury stock									(717)	(9,596)	(10,333)
Dividends paid									(6,960)	(5,172)	(3,369)
Proceeds from the exercise of stock options									279	517	28
Net cash from financing activities									99,399	178,612	137,480
Change in cash and cash equivalents									993	9,977	2,930
Cash and cash equivalents, beginning of period				45,887				35,910	45,887	35,910	32,980
Cash and cash equivalents, end of period	46,880				45,887				46,880	45,887	35,910
Parent Company [Member]
Cash Flows from Operating Activities
Net income									21,785	18,828	16,282
Adjustments to reconcile net income to net cash provided by operating activities:
(Increase) decrease in undistributed earnings of the subsidiaries									(7,479)	3,495	(1,943)
Decrease (increase) in deferred tax assets									682	(481)	(356)
(Increase) decrease in other assets									(5,666)	16	4
Increase (decrease) in other liabilities									(642)	154	86
Net cash from operating activities									8,680	22,012	14,073
Cash Flows from Investing Activities
Net cash disbursed in the acquisition of Ohio Legacy Corp.									(20,379)
Net cash from investing activities									(22,829)	(3,000)
Cash Flows from Financing Activities
Issuance of common stock, Long-term Incentive Plan									597
Purchase of treasury stock									(717)	(9,596)	(10,333)
Dividends paid									(6,960)	(5,172)	(3,369)
Proceeds from the exercise of stock options									279	517	28
Net cash from financing activities									(6,801)	(14,251)	(13,674)
Change in cash and cash equivalents									(20,950)	4,761	399
Cash and cash equivalents, beginning of period				$ 25,924				$ 21,163	25,924	21,163	20,764
Cash and cash equivalents, end of period	$ 4,974				$ 25,924				4,974	25,924	$ 21,163
Parent Company [Member] | HSB Insurance, Inc. [Member]
Cash Flows from Investing Activities
Equity investment									(450)
Parent Company [Member] | HSB Capital LLC [Member]
Cash Flows from Investing Activities
Equity investment									$ (2,000)	$ (3,000)