Employee Benefits and Stock Compensation - Employee Stock Purchase Plan (Details) - ESPP - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	15,225	12,434	10,483
Weighted-average employee purchase price (in dollars per share)	$ 26.85	$ 22.67	$ 16.02

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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