Stock Compensation - RSU and PSU award activity (Details)	6 Months Ended
	Jun. 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)	(92,732)
Cancelled (in shares)	29,459
Shares Available for Grant Ending Balance (in shares)	1,082,879
Shares Subject to Outstanding Options, Shares
Outstanding at the beginning of the period (in shares)	1,246,570
Granted (in shares)	92,732
Cancelled (in shares)	(29,459)
Released (in shares)	(284,903)
Outstanding at the end of the period (in shares)	981,564
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Granted (in dollars per share) | $ / shares	$ 120.36
Cancelled (in dollars per share) | $ / shares	85.80
Released (in dollars per share) | $ / shares	$ 119.64
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