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Parent Company Condensed Financial Statements (Condensed Balance Sheet - Additional Information) (Details) - $ / shares
Dec. 31, 2019
Dec. 31, 2018
Balance sheets    
Common stock, par value (in dollars per share) $ 0.001 $ 0.001
Common stock, shares authorized (in shares) 200,000,000 200,000,000
Common stock, shares issued (in shares) 166,621,959 165,867,587
Treasury stock, shares (in shares) 20,996,574 20,906,224
Parent Company    
Balance sheets    
Common stock, par value (in dollars per share) $ 0.001 $ 0.001
Common stock, shares authorized (in shares) 200,000,000 200,000,000
Common stock, shares issued (in shares) 166,621,959 165,867,587
Treasury stock, shares (in shares) 20,996,574 20,906,224