Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Line Items]
Provision for income taxes		$ 20,040	$ 1,647	$ 18,691	$ 10,297
Effective income tax rates		19.90%	1.70%	9.70%	5.80%
Federal statutory income tax rate				35.00%
Income tax provision from measurement of deferred tax assets		$ 19,900
Income tax benefit from assessment of valuation allowance		4,100
Excess tax benefits				$ 10,800
Lapse of statute of limitations		6,000	$ 9,400	7,900	$ 11,100
Unrecognized tax benefits		67,300		67,300			$ 63,700
Tax settlement, foreign jurisdiction		1,900
Accrued interest and penalties related to uncertain tax positions		2,100		2,100			3,000
Expected decrease in uncertain tax positions		21,400		21,400
Non-current income tax payable
Income Tax Disclosure [Line Items]
Unrecognized tax benefits		34,400		34,400			51,800
Current income tax payable
Income Tax Disclosure [Line Items]
Unrecognized tax benefits		$ 100		$ 100			$ 1,500
Subsequent Event | Scenario, Forecast
Income Tax Disclosure [Line Items]
Federal statutory income tax rate	21.00%					31.60%
Deferred Tax Asset | Maximum
Income Tax Disclosure [Line Items]
Federal statutory income tax rate		31.60%
Deferred Tax Asset | Maximum
Income Tax Disclosure [Line Items]
Federal statutory income tax rate		21.00%