Stock-Based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Thousands | 9 Months Ended | 12 Months Ended |
Sep. 30, 2015 | Sep. 30, 2014 | Dec. 31, 2014 |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] | | | |
Compensation expense, gross | $ 3,948 | $ 2,940 | |
Stock Options [Member] | | | |
Options, shares [Roll Forward] | | | |
Outstanding, beginning of period (in shares) | 9,875 | | |
Expired (in shares) | 0 | | |
Exercised (in shares) | (9,875) | | |
Forfeited, other (in shares) | 0 | | |
Outstanding, end of period (in shares) | 0 | | 9,875 |
Options exercisable, end of period (in shares) | 0 | | |
Options, weighted average exercise price [Roll Forward] | | | |
Outstanding, beginning of period (in dollars per share) | $ 10.99 | | |
Expired (in dollars per share) | 0 | | |
Exercised (in dollars per share) | 10.99 | | |
Forfeited, other (in dollars per share) | 0 | | |
Outstanding, end of period (in dollars per share) | 0 | | $ 10.99 |
Options exercisable, end of period (in dollars per share) | $ 0 | | |
Options, additional disclosures [Abstract] | | | |
Outstanding, weighted average remaining contractual term | 0 years | | 4 months 24 days |
Options exercisable, weighted average remaining contractual term, end of period | 0 years | | |
Total intrinsic value of options exercised | $ 300 | | |
Options granted (in shares) | 0 | | |
Performance-based Shares [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Measuring period for performance-based shares | 3 years | | |
Restricted Shares [Member] | Employees [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Estimated forfeitures | 5.00% | | |
Restricted Shares [Member] | Executives [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Estimated forfeitures | 0.00% | | |
Restricted Shares [Member] | Directors [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Estimated forfeitures | 0.00% | | |
Restricted Shares [Member] | Age 60 [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Vesting percentage | 25.00% | | |
Restricted Shares [Member] | Age 63 [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Vesting percentage | 25.00% | | |
Restricted Shares [Member] | Age65 [Member] | | | |
Restricted and Performance Stock Grants [Abstract] | | | |
Vesting percentage | 100.00% | | |
Restricted and Performance-based Shares [Member] | | | |
Restricted and performance-based stock, shares [Roll Forward] | | | |
Beginning of period (in shares) | 749,018 | | |
Granted (in shares) | 7,000 | | |
Vested (in shares) | (48,918) | | |
Forfeited (in shares) | (4,250) | | |
End of period (in shares) | 702,850 | | 749,018 |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] | | | |
Beginning of period (in dollars per share) | $ 24.62 | | |
Granted (in dollars per share) | 35.07 | | |
Vested (in dollars per share) | 33.07 | | |
Forfeited (in dollars per share) | 25.70 | | |
End of period (in dollars per share) | $ 24.13 | | $ 24.62 |
Compensation expense, gross | $ 3,600 | 2,500 | |
Compensation expense, net of tax | 2,300 | $ 1,600 | |
Unamortized compensation expense | $ 8,200 | | |
Restricted and Performance-based Shares [Member] | Employees [Member] | | | |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] | | | |
Weighted average period of recognition for unrecognized compensation expense | 4 years 6 months | | |
Restricted and Performance-based Shares [Member] | Directors [Member] | | | |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] | | | |
Weighted average period of recognition for unrecognized compensation expense | 7 months 6 days | | |