XML 28 R12.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Restrictions on Cash and Due from Bank Accounts | 12 Months Ended
--- | ---
Dec. 31, 2017
Cash and Cash Equivalents [Abstract] |
RESTRICTIONS ON CASH AND DUE FROM BANK ACCOUNTS | RESTRICTIONS ON CASH AND DUE FROM BANK ACCOUNTS The Board of Governors of the Federal Reserve System, or the Federal Reserve, imposes certain reserve requirements on all depository institutions. These reserves are maintained in the form of vault cash or as an interest-bearing balance with the Federal Reserve. The required reserves averaged $36.2 million for 2017, $36.8 million for 2016 and $44.1 million for 2015.

X
- Definition Cash reserve requirement of the Federal Reserve. + References No definition available. + Details
Name: | stba_RestrictionsOnCashAndDueFromBankAccountsTextBlock
Namespace Prefix: | stba_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_CashAndCashEquivalentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration