Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Class A	Preferred stock, $0.01 par value per share	Common stock	Common stock Common Class A	Common stock B-1 Common Stock	Additional paid-in capital	Additional paid-in capital Employee stock notes	Other Additional Capital	Retained earnings (accumulated deficit)	Accumulated other comprehensive (loss) income	Foreign currency adjustments	Unrealized (loss) gain on interest rate hedges	Net actuarial pension (loss) gain	Non-controlling interest	Common Class B-1 Converted Common stock Common Class A	Preferred Stock Converted Common stock Common Class A
Increase (Decrease) in Stockholders' Equity
Adoption of new accounting standard ASU 2016-09										$ 635
Balance at beginning of period at Dec. 31, 2016			$ 0		$ 178	$ 2		$ (843)	$ 37,205	222,232		$ (65,949)	$ (13,296)	$ (117,937)	$ 0
Balance at beginning of period, shares at Dec. 31, 2016			0		17,894,393	177,221
Increase (Decrease) in Stockholders' Equity
Shares issued for exercise/vesting of share-based compensation awards					$ 4				596
Shares issued for exercise/vesting of share-based compensation awards, shares					323,848
Shares repurchased		$ 0								0
Shares repurchased, shares		0
Stock converted to common stock						$ (2)			150,901							$ 3	$ 642
Stock converted to common stock, shares						(177,221)										309,404	64,211,172
Shares surrendered for tax obligations for employee share-based transactions					$ (1)				(2,883)
Shares surrendered for tax obligations for employee share-based transactions, shares					(87,836)
Shares issued					$ 223				480,306
Shares issued, shares					22,272,727
Costs associated with initial public offering									(7,923)
Amortization of share-based compensation									9,713
Net issuances, payments and accrued interest on notes								12
Net income	$ 53,206									53,206
Foreign currency change during period	55,631											55,631			0
Unrealized (loss) gain on interest rate hedges change during period	2,105												2,105
Acquisition of non-controlling interest															0
Net actuarial pension (loss) gain change during period	4,029													4,029	0
Balance at period end at Jul. 01, 2017	808,789			$ 1,049	$ 1,049	$ 0	$ 667,084	(831)	667,915	276,073	$ (135,417)	(10,318)	(11,191)	(113,908)	0
Balance at period end, shares at Jul. 01, 2017					104,923,708	0
Increase (Decrease) in Stockholders' Equity
Adoption of new accounting standard ASU 2016-09										0
Balance at beginning of period at Dec. 31, 2017	792,037		$ 0		$ 1,060	$ 0		(661)	653,327	233,658		21,985	(8,810)	(108,522)	0
Balance at beginning of period, shares at Dec. 31, 2017			0		105,990,483	0
Increase (Decrease) in Stockholders' Equity
Shares issued for exercise/vesting of share-based compensation awards					$ 6				189
Shares issued for exercise/vesting of share-based compensation awards, shares					576,406
Shares repurchased					$ (16)					(46,975)
Shares repurchased, shares				(1,643,917)
Stock converted to common stock						$ 0			0							$ 0	$ 0
Stock converted to common stock, shares						0										0	0
Shares surrendered for tax obligations for employee share-based transactions					$ (2)				(6,683)
Shares surrendered for tax obligations for employee share-based transactions, shares					(199,039)
Shares issued					$ 0				0
Shares issued, shares					0
Costs associated with initial public offering									0
Amortization of share-based compensation									7,958
Net issuances, payments and accrued interest on notes								26
Net income	75,723									75,776
Foreign currency change during period	(36,621)											(36,621)			16
Unrealized (loss) gain on interest rate hedges change during period	1,392												1,392
Acquisition of non-controlling interest															(184)
Net actuarial pension (loss) gain change during period	3,981													3,981	(53)
Balance at period end at Jun. 30, 2018	$ 790,847			$ 1,048	$ 1,048	$ 0	$ 654,156	$ (635)	$ 654,791	$ 262,459	$ (126,595)	$ (14,636)	$ (7,418)	$ (104,541)	$ (221)
Balance at period end, shares at Jun. 30, 2018					104,723,933	0