Stockholders’ equity Stockholders’ equity - $ / shares		12 Months Ended
	Mar. 27, 2014	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Jul. 01, 2015
Class of Stock [Line Items]
Common Stock, Shares, Issued		50,598,901	48,955,909		17,000,000
Preferred Stock, Shares Issued		0	0
Common stock, shares authorized (in shares)		100,000,000	100,000,000
Number of shares authorized to be repurchased				1,000,000
Stock repurchased in period (in shares)		0	0
Preferred Stock, Shares Authorized		5,000,000	50,000,000
Preferred Stock, Par or Stated Value Per Share		$ 0.01	$ 0.01
Preferred Stock, Shares Outstanding		0	0
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Common stock, shares outstanding (in shares)		50,598,901	48,955,909
Preferred Share Purchase Right
Class of Stock [Line Items]
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Preferred share purchase rights dividend (shares)	1
Exercise price of rights (USD per share)	$ 30.00
Series B Junior Participating Preferred Stock
Class of Stock [Line Items]
Number of securities called by each right (shares)	0.001
Preferred Stock
Class of Stock [Line Items]
Number of securities called by each right (shares)	0.001