Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Details)

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Stockholders' Equity (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
May. 06, 2015
May. 06, 2014
Sep. 30, 2015
Sep. 30, 2015
Dec. 31, 2014
May. 31, 2015
May. 31, 2014
Class of Stock [Line Items]              
Authorized amount of common stock repurchase   $ 50,000,000       $ 50,000,000.0 $ 75,000,000.0
Repurchase period 1 year 1 year          
Number of shares repurchased     807,922 1,579,226 966,595    
Weighted average cost per share of shares repurchased     $ 18.95 $ 19.28 $ 16.06    
Value of stock repurchased     $ 15,300,000 $ 30,455,000 $ 15,500,000    
Common Stock              
Class of Stock [Line Items]              
Number of shares retired during the period       2,545,821