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Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Parenthetical) (Details) - Common Stock - shares
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Class Of Stock [Line Items]    
Stock repurchase, shares   135,000
Share Repurchase Program August 2017    
Class Of Stock [Line Items]    
Stock repurchase, shares 86,168