Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Details)

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Stockholders' Equity (Details) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
May. 06, 2015
May. 06, 2014
Jun. 30, 2015
Jun. 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     369,861 771,304 966,595    
Weighted average cost per share of shares repurchased     $ 19.46 $ 19.64 $ 16.06    
Value of stock repurchased     $ 7,200,000 $ 15,146,000 $ 15,500,000    
Common Stock              
Class of Stock [Line Items]              
Number of shares retired during the period       (1,737,899)