Share-Based Payments - Stock Option Plan 2015 Outstanding and Fair Value (Details) - Stock Option Plan 2015 - USD ($)			3 Months Ended
	Mar. 21, 2017	Feb. 07, 2017	Mar. 31, 2017
Share-Based Payments
Share-based compensation expense (in dollars)			$ 1,800,000
Income tax benefit			$ 200,000
Weighted-average grant date fair value (in dollars per share)			$ 32.47
Granted (in shares)			102,560
Fair Value Assumptions
Grant date share price (in dollars per share)	$ 110.00	$ 85.00
Exercise price (in dollars per share)	$ 110.00	$ 85.00	$ 85.51
Expected volatility (as a percent)	66.00%	68.00%
Expected option term (in years)	2 years 2 months 12 days	2 years 2 months 12 days
Risk-free interest rate (as a percent)	(0.718%)	(0.777%)
Other disclosures
Weighted-average remaining contractual life			9 years 10 months 24 days
Total unrecognized compensation related to non-vested options (in dollars)			$ 8,000,000
Period of recognition of total unrecognized compensation related to options			2 years 2 months 12 days