CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($)
$ in Thousands
Total
Common Stock - Class A
Additional Paid-in Capital
Accumulated Other Comprehensive Income (Loss)
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Cumulative effect of change in accounting principle $ 903   $ 388   $ 515
Beginning balance at Dec. 31, 2016 475,509 $ 591 576,927 $ (5,287) (96,722)
Beginning balance (in shares) at Dec. 31, 2016   59,145,000      
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Common stock: class A shares issued related to warrants [1] $ 183   183    
Common stock: class A shares issued related to warrants (in shares) 32,368 32,000 [1]      
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes $ (1,480) $ 14 (1,494)    
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)   1,341,000      
Share-based compensation expense 9,484   9,484    
Change in unrealized investment gains/losses, net of tax 2,428     2,428  
Net income 22,050       22,050
Ending balance at Dec. 31, 2017 509,077 $ 605 585,488 (2,859) (74,157)
Ending balance (in shares) at Dec. 31, 2017   60,518,000      
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Cumulative effect of change in accounting principle 0     282 (282)
Common stock: class A shares issued related to public offering 79,165 $ 43 79,122    
Common stock: class A shares issued related to public offering (in shares)   4,255,000      
Common stock: class A shares issued related to warrants [1] $ 552   552    
Common stock: class A shares issued related to warrants (in shares) 29,437 29,000 [1]      
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes $ (104) $ 10 (114)    
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)   952,000      
Share-based compensation expense 5,822   5,822    
Change in unrealized investment gains/losses, net of tax (12,466)     (12,466)  
Net income 47,596        
Ending balance at Jun. 30, 2018 $ 629,642 $ 658 $ 670,870 $ (15,043) $ (26,843)
Ending balance (in shares) at Jun. 30, 2018   65,754,000      
[1] During the year ended December 31, 2017 and the six months ended June 30, 2018, we issued 32,368 and 29,437 common shares, respectively, with a par value of $0.01 related to the exercise of warrants, which is not identifiable in this schedule due to rounding.