Stockholders' Equity - Stock Repurchases (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Common share repurchases (in shares)	21,202	19,058	20,689
Treasury stock repurchased (in dollars per share)	$ 28.59	$ 28.01	$ 29.64

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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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration