Stock Compensation Plans (Details 2) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Time-Based RSUs
Shares
Outstanding at beginning of period (in shares) | shares	1,218,714
Granted (in shares) | shares	336,582
Vested (in shares) | shares	(284,479)
Forfeited (in shares) | shares	(94,346)
Outstanding at end of period (in shares) | shares	1,176,471
Weighted Average Grant-Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 35.92
Granted (in dollars per share) | $ / shares	54.47
Vested (in dollars per share) | $ / shares	36.80
Forfeited (in dollars per share) | $ / shares	39.86
Outstanding at end of period (in dollars per share) | $ / shares	$ 40.70
Total unrecognized compensation cost | $	$ 31.0
Weighted average period to recognize unrecognized compensation cost	2 years 1 month 7 days
Performance-Based RSUs
Shares
Outstanding at beginning of period (in shares) | shares	410,746
Granted (in shares) | shares	131,597
Vested (in shares) | shares	(118,044)
Forfeited (in shares) | shares	0
Outstanding at end of period (in shares) | shares	424,299
Weighted Average Grant-Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 35.27
Granted (in dollars per share) | $ / shares	56.59
Vested (in dollars per share) | $ / shares	36.85
Forfeited (in dollars per share) | $ / shares	0.00
Outstanding at end of period (in dollars per share) | $ / shares	$ 41.44
Total unrecognized compensation cost | $	$ 17.8
Weighted average period to recognize unrecognized compensation cost	2 years 2 months 15 days