Consolidated Statements of Changes In Shareholders' Equity (Parenthetical) - $ / shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Statement of Stockholders' Equity [Abstract]
Cash dividends (in dollars per share)	$ 1.05	$ 0.90
Common Stock \| Class A Common Stock
Stock repurchased during period (in shares)	125,000	0

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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-Name Accounting Standards Codification
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration