Employee Benefit Plans - Narrative (Detail) - USD ($)	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Benefits Disclosure [Line Items]
Other non-operating expense, net						$ 1,910,000			$ 7,532,000	$ 7,331,000	$ 68,110,000	$ 31,959,000
Other selling and administrative expenses	$ (398,253,000)	$ (325,874,000)	$ (360,000,000)	$ (424,617,000)	$ (452,644,000)	(381,214,000)	$ (353,296,000)	$ (330,829,000)	(1,065,339,000)	(1,508,744,000)	(1,517,983,000)	(1,391,769,000)
Accumulated benefit obligation of defined benefit pension plans	549,700,000				$ 618,500,000					549,700,000	$ 618,500,000
Total estimated cash contributions to be made during the next fiscal year for defined benefit pension and postretirement benefit plans	$ 6,000,000									$ 6,000,000
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%						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	$ 68,300,000				$ 76,600,000					$ 68,300,000	$ 76,600,000
Cash surrender value of life insurance policies	$ 65,800,000				67,900,000					65,800,000	67,900,000
Expense for incentive compensation plans										$ 84,100,000	19,400,000	16,500,000
January 1, 2016 to December 31, 2018 LTIP | Performance-Related Component
Employee Benefits Disclosure [Line Items]
Performance cycle										3 years
Number Of Shares Earned For Performance Related Component Of Performance Restricted Stock Units										0
Weighted average grant date fair value of restricted stock units granted (in USD per share)										$ 32.60
Expense recognized for restricted stock units												2,800,000
Cumulative EPS target										3 years
January 1, 2016 to December 31, 2018 LTIP | Market-Related Component
Employee Benefits Disclosure [Line Items]
Weighted average grant date fair value of restricted stock units granted (in USD per share)										$ 5.10
Expense recognized for restricted stock units										$ 0	$ 400,000	$ 400,000
January 1, 2017 to December 31, 2019 LTIP
Employee Benefits Disclosure [Line Items]
Number of shares that can be earned for each of the three years for the performance-related component of performance restricted stock units - range of possible outcomes - (low-end) (in shares)										100,000.0
Number of shares that can be earned for each of the three years for the performance-related component of performance restricted stock units - range of possible outcomes - (high-end) (in shares)										200,000
Adjustment (for the market-related component) to the results of the performance-related component of performance restricted stock units over the three-year performance cycle - range of possible outcomes - upward adjustment - (high-end) (in shares)										100,000
Adjustment (for the market-related component) to the results of the performance-related component of performance restricted stock units over the three-year performance cycle - range of possible outcomes - downward adjustment - (low-end) (in shares)										100,000
January 1, 2017 to December 31, 2019 LTIP | Performance-Related Component
Employee Benefits Disclosure [Line Items]
Performance cycle										3 years
Weighted average grant date fair value of restricted stock units granted (in USD per share)										$ 13.24	$ 21.60
Expense recognized for restricted stock units											$ 0
January 1, 2017 to December 31, 2019 LTIP | Market-Related Component
Employee Benefits Disclosure [Line Items]
Weighted average grant date fair value of restricted stock units granted (in USD per share)										$ 1.46	$ 1.46
Expense recognized for restricted stock units										$ 300,000	$ 0
January 1, 2017 to December 31, 2019 LTIP | Performance Shares Market Related Component
Employee Benefits Disclosure [Line Items]
Expense recognized for restricted stock units										$ 200,000
January 1, 2018 to December 31, 2020 LTIP
Employee Benefits Disclosure [Line Items]
Number of shares that can be earned for each of the three years for the performance-related component of performance restricted stock units - range of possible outcomes - (low-end) (in shares)										0
Number of shares that can be earned for each of the three years for the performance-related component of performance restricted stock units - range of possible outcomes - (high-end) (in shares)										1,700,000
January 1, 2018 to December 31, 2020 LTIP | Performance-Related Component
Employee Benefits Disclosure [Line Items]
Weighted average grant date fair value of restricted stock units granted (in USD per share)										$ 15.08
January 1, 2018 to December 31, 2020 LTIP | Performance Shares Market Related Component
Employee Benefits Disclosure [Line Items]
Expense recognized for restricted stock units										$ 2,700,000
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	$ 6,300,000									$ 6,300,000
Long-term rate of return on plan assets used to determine net periodic benefit cost for domestic defined benefit pension plans										6.00%	6.30%	6.50%
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	(2,400,000)									$ (2,400,000)
Restatement Adjustment
Employee Benefits Disclosure [Line Items]
Other non-operating expense, net						0			0	0	$ 0	$ 0
Other selling and administrative expenses	$ (3,948,000)		$ 0		0	0	0	0	$ 0	(3,948,000)	0	0
Restatement Adjustment | January 1, 2016 to December 31, 2018 LTIP | Performance-Related Component
Employee Benefits Disclosure [Line Items]
Expense recognized for restricted stock units										$ (2,800,000)
Accounting Standards Update 2017-07
Employee Benefits Disclosure [Line Items]
Other non-operating expense, net					1,800,000	500,000	(300,000)	1,400,000			3,400,000	8,400,000
Other selling and administrative expenses					$ 1,800,000	$ 500,000	$ (300,000)	$ 1,400,000			$ 3,400,000	$ 8,400,000