Stockholders' Equity - Common Stock Repurchased (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Shares repurchased related to employee stock-based compensation plans (in shares)	3,087,396	3,358,417	3,354,730
Average purchase price per share (in dollars per share)	$ 11.32	$ 11.96	$ 7.83
Common shares issued (in shares)	6,392,634	6,831,108	5,955,045

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Balance Type:	na
Period Type:	duration