Employee Stock Benefit Plans - Workforce Reduction (Details) $ in Thousands			3 Months Ended			6 Months Ended
	Jun. 27, 2018 employee	Jan. 30, 2018 employee	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Workforce Reduction
Share-based compensation expense			$ 10,752		$ 9,140	$ 19,794	$ 16,419
Restructuring
Workforce Reduction
Share-based compensation expense			413			$ 607
Reduction in Field-based Workforce, January 30, 2018
Workforce Reduction
Number of employees eliminated | employee		60
Reduction in Field-based Workforce, January 30, 2018 | Restructuring | Employee severance, benefits and related costs
Workforce Reduction
Share-based compensation expense				$ 200
Reduction in Headquarter-based Workforce, June 27, 2018
Workforce Reduction
Number of employees expected to be eliminated | employee	40
Reduction in Headquarter-based Workforce, June 27, 2018 | Restructuring | Employee severance, benefits and related costs
Workforce Reduction
Share-based compensation expense			$ 400