Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 26,889,000	$ 30,019,000	$ 87,678,000	$ 88,160,000
Effective tax rate	20.20%	26.40%	21.90%	26.60%
Deferred tax liability, provisional income tax benefit					$ 40,600,000
Accumulated foreign earnings, provisional liability	$ 30,400,000		$ 30,400,000		30,300,000
Transition tax for accumulated foreign earnings, increase (decrease) in provisional income tax expense			100,000
Transition tax liability						$ 6,400,000
Provisional increase, deferred tax liability, income tax (expense) benefit	7,800,000				9,200,000
Adjustment, deferred income tax expense (benefit)	1,400,000				9,200,000
Permanent reinvestment, deferred tax liability, income tax (expense) benefit					$ 10,800,000
Minimum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible change in unrecognized tax benefits over next 12 months	0		0
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible change in unrecognized tax benefits over next 12 months	$ 1,300,000		$ 1,300,000