Stock Compensation - RSU and PSU award activity (Details)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Restricted Stock Units (RSUs)
Shares Available For Grant
Shares Available for Grant Beginning Balance (in shares)	1,146,152
Granted (in shares)	(396,331)
Cancelled (in shares)	41,376
Shares Available for Grant Ending Balance (in shares)	791,197
Shares Subject to Outstanding Options, Shares
Outstanding at the beginning of the period (in shares)	1,246,570
Granted (in shares)	396,331
Cancelled (in shares)	(41,376)
Released (in shares)	(382,133)
Outstanding at the end of the period (in shares)	1,176,016
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 82.05
Granted (in dollars per share) | $ / shares	126.45
Cancelled (in dollars per share) | $ / shares	89.68
Released (in dollars per share) | $ / shares	127.72
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 100.86
Performance Stock Units (PSUs)
Shares Available For Grant
Shares Available for Grant Ending Balance (in shares)	0
Shares Subject to Outstanding Options, Shares
Released (in shares)	(43,376)
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Released (in dollars per share) | $ / shares	$ 122.29