Stockholders' Equity - ESPP Activity (Details) - ESPP - shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-Based Compensation Arrangement By Share-Based Payment Award, Shares Available [Roll Forward]
Beginning Balance, Equity securities available (shares)	208,159	228,279	246,039
Less: common stock purchased by eligible employees (shares)	(23,299)	(20,120)	(17,760)
Ending Balance, Equity securities available (shares)	184,860	208,159	228,279

Number of share options (or share units) exercised during the current period.

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