Equity Compensation - RSU Rollforward (Details) - Restricted Stock shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Shares
Restricted Shares, Beginning Balance | shares	185
Restricted Shares, Granted | shares	86
Incremental Performance Shares | shares	3
Restricted Shares, Forfeited | shares	(7)
Restricted Shares, Vested | shares	(86)
Restricted Shares, Ending Balance | shares	181
Weighted Average Grant Date Fair Value
Weighted Average Grant-Date Fair Value, Beginning Balance (in dollars per share) | $ / shares	$ 59.21
Weighted Average Grant-Date Fair Value, Granted (in dollars per share) | $ / shares	78.52
Weighted Average Grant-Date Fair Value, Incremental Performance Shares | $ / shares	50.59
Weighted Average Grant-Date Fair Value, Forfeited (in dollars per share) | $ / shares	69.14
Weighted Average Grant-Date Fair Value, Vested (in dollars per share) | $ / shares	56.45
Weighted Average Grant-Date Fair Value, Ending Balance (in dollars per share) | $ / shares	$ 69.11
Additional disclosures
Initial target percentage	100.00%
Payout percentage result	122.00%