Earnings Per Share (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Basic:    
Net income attributable to common stockholders $ 6,410 $ 10,274
Weighted average number of common shares outstanding 17,302,522 17,054,598
Basic net income per share attributable to common stockholders $ 0.37 $ 0.60
Diluted:    
Net income attributable to common stockholders $ 6,410 $ 10,274
Weighted average number of common shares outstanding 17,302,522 17,054,598
Weighted average number of dilutive common share equivalents from options to purchase common stock 412,891 512,985
Common shares and common share equivalents 17,715,413 17,567,583
Diluted net income per share $ 0.36 $ 0.58
Stock Options [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Total number of stock options excluded from diluted shares computation 349,117