Employee Benefit Plans - Narrative (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) incentive_program	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) incentive_program	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Employee Benefits Disclosure [Line Items]
Other selling and administrative expenses	$ (418,414)	$ (365,961)	$ (308,311)	$ (297,336)	$ (398,253)	$ (325,874)	$ (360,000)	$ (424,617)	$ (1,390,022)	$ (1,508,744)	$ (1,517,983)
Accumulated benefit obligation of defined benefit pension plans	608,400				549,700				608,400	549,700
Total estimated cash contributions to be made during the next fiscal year for defined benefit pension and postretirement benefit plans	$ 11,000								$ 11,000
Percentage of domestic defined benefit pension plan assets to total defined benefit pension plan assets	77.00%								77.00%
Percentage of total membership in pension plan insured											40.00%
Percentage limitation of an employee's total account balance that may be allocated to the Mattel Stock Fund in the Mattel, Inc. Personal Investment Plan	25.00%								25.00%
Liability for deferred compensation and excess benefit plans	$ 65,200				68,300				$ 65,200	68,300
Cash surrender value of life insurance policies	$ 75,700				$ 65,800				75,700	65,800
Expense for incentive compensation plans									$ 119,500	84,100	$ 19,400
Number of long-term incentive programs | incentive_program	3								3
Long-term Incentive Program
Employee Benefits Disclosure [Line Items]
Long term incentive compensation expenses									$ 11,000	$ 3,000	$ 600
U.S. equity securities
Employee Benefits Disclosure [Line Items]
Target allocation for domestic defined benefit pension plan assets	42.00%								42.00%
Non US Equity Securities
Employee Benefits Disclosure [Line Items]
Target allocation for domestic defined benefit pension plan assets	28.00%								28.00%
Long-Term Bond Securities
Employee Benefits Disclosure [Line Items]
Target allocation for domestic defined benefit pension plan assets	20.00%								20.00%
US Treasury Securities
Employee Benefits Disclosure [Line Items]
Target allocation for domestic defined benefit pension plan assets	10.00%								10.00%
Defined benefit pension plans
Employee Benefits Disclosure [Line Items]
Estimated net actuarial loss (gain) and prior service credit that will be amortized from accumulated other comprehensive loss into net periodic benefit cost in next fiscal year	$ 8,500								$ 8,500
Long-term rate of return on plan assets used to determine net periodic benefit cost for domestic defined benefit pension plans									6.00%	6.00%	6.30%
Postretirement benefit plans
Employee Benefits Disclosure [Line Items]
Estimated net actuarial loss (gain) and prior service credit that will be amortized from accumulated other comprehensive loss into net periodic benefit cost in next fiscal year	$ (2,100)								$ (2,100)
Accounting Standards Update 2017-07
Employee Benefits Disclosure [Line Items]
Other selling and administrative expenses											$ 3,400