Stock Compensation - Summary of Stock Option Activity (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Non-vested restricted stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	405,536
Restricted stock units granted (in shares) | shares	131,341
Vested and paid (in shares) | shares	(107,631)
Forfeited (in shares) | shares	(541)
Ending balance (in shares) | shares	428,705
Weighted Average Price
Beginning balance (in dollars per share) | $ / shares	$ 44.58
Granted (in dollars per share) | $ / shares	51.83
Vested (in dollars per share) | $ / shares	61.59
Forfeited (in dollars per share) | $ / shares	49.58
Ending balance (in dollars per share) | $ / shares	$ 42.52
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	400,037
Restricted stock units granted (in shares) | shares	158,262
Vested and paid (in shares) | shares	(112,710)
Forfeited (in shares) | shares	(735)
Ending balance (in shares) | shares	444,854
Weighted Average Price
Beginning balance (in dollars per share) | $ / shares	$ 55.65
Granted (in dollars per share) | $ / shares	68.08
Vested (in dollars per share) | $ / shares	83.94
Forfeited (in dollars per share) | $ / shares	60.33
Ending balance (in dollars per share) | $ / shares	$ 52.90