Employee Benefit Plans - Stock Option Valuation Assumptions (Details) - $ / shares	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Benefits and Share-based Compensation, Noncash [Abstract]
Number of options granted (shares)	0	0	114,500	47,100
Weighted average exercise price (in dollars per share)	$ 0.00	$ 0.00	$ 20.24	$ 16.37
Weighted average fair value of options (in dollars per share)	$ 0.00	$ 0.00	$ 5.97	$ 4.64
Expected life	0 years	0 years	6 years 4 months 6 days	6 years 6 months 26 days
Expected volatility	0.00%	0.00%	26.40%	28.12%
Risk-free interest rate	0.00%	0.00%	2.48%	2.18%
Dividend yield	0.00%	0.00%	1.14%	1.15%

No definition available.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

+ References

No definition available.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Name Accounting Standards Codification
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-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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