Capital Stock - Narratives (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended
	Feb. 01, 2017	Jun. 30, 2018	Jun. 30, 2018	Jul. 01, 2017	Apr. 30, 2018	Dec. 31, 2017	Jan. 31, 2017	Jan. 03, 2017	Dec. 31, 2016
Class of Stock
Common stock authorized (shares)	900,000,000	900,000,000	900,000,000			900,000,000		900,000,000
Common stock, par value (usd per share)	$ 0.01	$ 0.01	$ 0.01			$ 0.01		$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	90,000,000	90,000,000	90,000,000			90,000,000	8,750,000
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01	$ 0.01			$ 0.01	$ 0.01
Shares held in employee trust (shares)		193,941	193,941			193,941
Shares held in employee trust (value)		$ 12,400	$ 12,400			$ 12,400
Proceeds from the sale of common stock, net of underwriting fees and commissions	$ 480,300		$ 0	$ 480,306
Cost associated with initial public offering	7,900
Capitalized initial public offering cost	$ 5,900
IPO
Class of Stock
Common stock authorized (shares)									22,810,000
Common Stock
Class of Stock
Common stock authorized (shares)	900,000,000								22,379,800
Common stock, par value (usd per share)	$ 0.01
Conversion of stock (shares)	309,404
Shares repurchased, shares				0
B-1 Common Stock
Class of Stock
Common stock authorized (shares)									430,200
Common stock
Class of Stock
Share authorized for repurchase (shares)					250,000,000
Shares repurchased, shares		1,643,917	1,643,917
Shares repurchased (usd per share)		$ 28.58	$ 28.58