Stock-Based Incentive Plans - Narrative (Details) $ / shares in Units, $ in Millions				6 Months Ended		12 Months Ended
	May 16, 2017 shares	May 15, 2017 $ / shares	Feb. 04, 2017 $ / shares shares	Jun. 30, 2017 USD ($) plan shares	Jun. 30, 2016 USD ($)	Dec. 31, 2016 shares
Stock-Based Compensation
Number of stock-based incentive plans | plan				1
Number of stock option plans superseded | plan				2
Granted (in shares) | shares				0		0
Total intrinsic value of options exercised (in dollars) | $				$ 0.5	$ 0.7
Unrecognized compensation cost and vesting period
Unrecognized compensation costs related to unvested share-based compensation arrangements | $				$ 17.8
Weighted-average period for recognition of unrecognized stock-based compensation expense				2 years 3 months 50 days
Restricted Stock Units
Stock-Based Compensation
Awarded (in shares) | shares			606,299	616,000
Total intrinsic value of awards vested (in dollars) | $				$ 11.3	$ 10.7
Non Employee Directors | Restricted Stock Units
Stock-Based Compensation
Awarded (in shares) | shares	10,066
Weighted average granted date fair value (in dollars per share) | $ / shares		$ 41.52	$ 43.42