Stockholders' equity (deficit) Share Repurchase (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2015	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015	Feb. 01, 2018	Feb. 29, 2016	Oct. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Common stock share repurchase program amount						$ 30,000
Number of shares authorized to be repurchased						702,239
Weighted average price per share (in dollars per share)			$ 42.72
Increase in treasury stock		$ 127,186	$ 55,000	$ 625,041
Accumulated deficit
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and retired during period		$ 108,300		469,500
Common stock
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and retired during period				$ 599,000
Retirement of treasury stock (shares)		2,271,448	1,707,000	12,833,178
Additional paid-in capital
Equity, Class of Treasury Stock [Line Items]
Increase in treasury stock		$ 0	$ (25,000)	$ 25,000
Adjustments to additional paid in capital, other				25,000
Stock repurchased and retired during period		18,900		129,400
Treasury stock, at cost
Equity, Class of Treasury Stock [Line Items]
Increase in treasury stock		$ 127,186	$ 80,000	$ 600,041
Common stock
Equity, Class of Treasury Stock [Line Items]
Repurchased stock		513,880	520,631	2,106,881,000
Average cost per share		$ 52.90	$ 48.02	$ 47.47
February 2015 ASR Agreement
Equity, Class of Treasury Stock [Line Items]
Common stock share repurchase program amount				$ 400,000
Number of shares authorized to be repurchased				8,226,297
Weighted average price per share (in dollars per share)	$ 48.62
October 2015 ASR Agreement
Equity, Class of Treasury Stock [Line Items]
Common stock share repurchase program amount							$ 125,000
Number of shares authorized to be repurchased			483,913				2,527,167
Weighted average price per share (in dollars per share)			$ 41.51
Percentage of total shares expected to be repurchased							80.00%
October 2015 ASR Agreement | Accumulated deficit
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and retired during period			$ 64,100
October 2015 ASR Agreement | Common stock
Equity, Class of Treasury Stock [Line Items]
Retirement of treasury stock (shares)			1,706,783
October 2015 ASR Agreement | Additional paid-in capital
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and retired during period			$ 15,900
October 2015 ASR Agreement | Treasury stock, at cost
Equity, Class of Treasury Stock [Line Items]
Increase in treasury stock			$ 80,000
May 2017 ASR Agreement
Equity, Class of Treasury Stock [Line Items]
Common stock share repurchase program amount		$ 100,000
Number of shares authorized to be repurchased		1,757,568
Weighted average price per share (in dollars per share)		$ 56.90
Subsequent event | February 2018 ASR Agreement
Equity, Class of Treasury Stock [Line Items]
Common stock share repurchase program amount					$ 650,000
Number of shares authorized to be repurchased					8,478,722
Percentage of total shares expected to be repurchased					80.00%