Net investments in consolidated subsidiary.

No definition available.

Name:	stba_NetInvestmentsInConsolidatedSubsidiary
Namespace Prefix:	stba_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3521-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3044-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=121583591&loc=SL98516268-108586

Parent Company Condensed Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Sep. 11, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net Income		$ 24,176	$ 16,705	$ (33,072)	$ 13,231	$ 22,269	$ 26,936	$ 26,101	$ 22,929	$ 21,040	$ 98,234	$ 105,334
Net Cash Provided by Operating Activities										53,451	138,423	128,017
INVESTING ACTIVITIES
Net Cash Provided by (Used in) in Investing Activities										(161,101)	(210,556)	(201,964)
FINANCING ACTIVITIES
Sale of treasury shares, net										(594)	(915)	(657)
Purchase of treasury shares										(12,559)	(18,222)	(12,256)
Cash dividends paid to common shareholders										(43,949)	(37,360)	(34,539)
Payment to repurchase of warrant	$ (7,700)									0	0	(7,652)
Net Cash Provided by Financing Activities										139,493	114,467	112,284
Net increase (decrease) in cash and cash equivalents										31,843	42,334	38,337
Cash and cash equivalents at beginning of year					197,823				155,489	197,823	155,489	117,152
Cash and Cash Equivalents at End of Year		229,666				197,823				229,666	197,823	155,489
Parent Company
OPERATING ACTIVITIES
Net Income										21,040	98,234	105,334
Equity in undistributed (earnings) losses of subsidiaries										33,430	(43,164)	(64,366)
Other										1,708	(99)	1,695
Net Cash Provided by Operating Activities										56,178	54,971	42,663
INVESTING ACTIVITIES
Net investments in subsidiaries										0	176	0
Acquisitions										0	(10)	0
Net Cash Provided by (Used in) in Investing Activities										0	166	0
FINANCING ACTIVITIES
Sale of treasury shares, net										(594)	(915)	(657)
Purchase of treasury shares										(12,559)	(18,222)	(12,256)
Cash dividends paid to common shareholders										(43,949)	(37,360)	(34,539)
Payment to repurchase of warrant										0	0	(7,652)
Net Cash Provided by Financing Activities										(57,102)	(56,497)	(55,104)
Net increase (decrease) in cash and cash equivalents										(924)	(1,360)	(12,441)
Cash and cash equivalents at beginning of year					$ 7,509				$ 8,869	7,509	8,869	21,310
Cash and Cash Equivalents at End of Year		$ 6,585				$ 7,509				$ 6,585	$ 7,509	$ 8,869