CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 70,099	$ 44,667	$ 179,842	$ 100,409
Other comprehensive gain:
Foreign currency translation gain (loss)	1,534	5,673	(5,695)	11,704
Income tax (expense) benefit on foreign currency translation gain (loss)	(390)	(2,206)	1,443	(4,559)
Foreign currency translation gain (loss), net of taxes	1,144	3,467	(4,252)	7,145
Gain on derivatives	2,904	4,105	15,201	8,482
Income tax expense on gain on derivatives	(736)	(1,601)	(3,855)	(3,308)
Gain on derivatives, net of taxes	2,168	2,504	11,346	5,174
Total other comprehensive gain	3,312	5,971	7,094	12,319
Comprehensive income	73,411	50,638	186,936	112,728
Net loss attributable to the noncontrolling interest	33	52	122	135
Foreign currency translation loss (gain), net of taxes attributable to the noncontrolling interest	33	(113)	406	(72)
Comprehensive loss (income) attributable to the noncontrolling interest	66	(61)	528	63
Comprehensive income attributable to Weight Watchers International, Inc.	$ 73,477	$ 50,577	$ 187,464	$ 112,791