ORRSTOWN FINANCIAL SERVICES, INC. (PARENT COMPANY ONLY) CONDENSED FINANCIAL INFORMATION - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 16,924	$ 12,805	$ 8,090
Adjustments to reconcile net income to cash provided by (used in) operating activities:
Deferred income taxes	1,776	543	3,078
Share-based compensation	1,586	1,493	1,386
Net change in other assets	2,053	535	52
Net cash provided by operating activities	9,090	22,487	16,350
Cash flows from investing activities:
Net cash provided by (used in) investing activities	18,962	(139,396)	(145,892)
Cash flows from financing activities:
Dividends paid	(6,150)	(4,375)	(3,488)
Net cash (used in) provided by financing activities	(60,405)	175,917	129,076
Net (decrease) increase in cash and cash equivalents	(32,353)	59,008	(466)
Cash and cash equivalents at beginning of year	88,815	29,807	30,273
Cash and cash equivalents at end of year	56,462	88,815	29,807
Consolidated
Cash flows from operating activities:
Net income	16,924	12,805	8,090
Adjustments to reconcile net income to cash provided by (used in) operating activities:
Amortization	47	3	0
Deferred income taxes	16	22	16
Equity in undistributed income of subsidiaries	(19,379)	(11,089)	(9,282)
Share-based compensation	236	205	247
Net change in other liabilities	(423)	12	(35)
Net change in other assets	311	2,039	(377)
Net cash provided by operating activities	(2,268)	3,997	(1,341)
Cash flows from investing activities:
Capital contributed to subsidiaries	(100)	0	(6,100)
Net cash paid for acquisitions	(8,142)	(4,597)	0
Net cash provided by (used in) investing activities	(8,242)	(4,597)	(6,100)
Cash flows from financing activities:
Dividends paid	(6,150)	(4,375)	(3,488)
Proceeds from issuance of subordinated notes, net of costs	0	31,857	0
Proceeds from issuance of common stock	1,463	1,448	1,276
Payments to repurchase common stock	(1,772)	(651)	0
Other, net	(59)	0	0
Net cash (used in) provided by financing activities	(6,518)	28,279	(2,212)
Net (decrease) increase in cash and cash equivalents	(17,028)	27,679	(9,653)
Cash and cash equivalents at beginning of year	28,596	917	10,570
Cash and cash equivalents at end of year	$ 11,568	$ 28,596	$ 917