Income Taxes (Details) - USD ($)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 29,615,000		$ 29,613,000	$ 60,789,000	$ 58,141,000
Effective tax rate	21.70%		26.10%	22.80%	26.70%
Deferred tax liability, provisional income tax benefit		$ 40,600,000
Accumulated foreign earnings, provisional liability	$ 30,400,000	$ 30,300,000		$ 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	$ 1,500,000			$ 1,500,000