Additional Senior Notes Available for Request

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- Definition

Debt Instrument, Covenant, Consolidated Leverage Ratio, Maximum

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- Definition

Debt Instrument, Covenant, Fixed Charges Coverage Ratio, Minimum

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount of assets pledged to secure a debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Amount of the required periodic payments including both interest and principal payments.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The effective interest rate during the reporting period.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Long-Term Debt - Additional Information (Details)		3 Months Ended		9 Months Ended
Long-Term Debt - Additional Information (Details)	Jan. 22, 2016 GBP (£)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 GBP (£)	Sep. 30, 2017 USD ($)	Dec. 31, 2017
Debt Instrument [Line Items]
Weighted average revolving interest rate, percentage				3.33%	3.33%
Line of credit facility, remaining borrowing capacity		$ 341,700,000		$ 341,700,000
Line of credit facility, maximum borrowing capacity		600,000,000.0		600,000,000.0
Gain (Loss) on Extinguishment of Debt		(1,494,000)	$ 0	(1,494,000)		$ 0
Debt instrument, collateral amount		400,000		400,000
Standby Letters of Credit
Debt Instrument [Line Items]
Proceeds from lines of credit		11,100,000		11,100,000
Senior Revolving Credit Facility Maturing in 2023 \| Standby Letters of Credit
Debt Instrument [Line Items]
Proceeds from lines of credit		$ 3,000,000		$ 3,000,000
2006 Senior Notes Payable Through 2021, 5.41%
Debt Instrument [Line Items]
Debt instrument, stated interest rate percentage		5.41%		5.41%			5.41%
Gain (Loss) on Extinguishment of Debt		$ 1,500,000
Notes Payable \| Multi-currency Notes Due in 2031
Debt Instrument [Line Items]
Aggregate principal amount	£ 54,900,000.0	71,500,000		$ 71,500,000
Annual installment debt payments				7,900,000	£ 6,100,000.0
Debt instrument, stated interest rate percentage	3.40%
Additional Senior Notes Available for Request		$ 150,000,000		$ 150,000,000
Minimum fixed charges coverage ratio (not less than)	1.50
Maximum consolidated leverage ratio (not to exceed)	3.50
Federal Funds Open Rate \| Senior Revolving Credit Facility Maturing in 2023
Debt Instrument [Line Items]
Interest rate margin, percentage				0.50%	0.50%
Overnight Bank Funding Rate \| Senior Revolving Credit Facility Maturing in 2023
Debt Instrument [Line Items]
Interest rate margin, percentage				0.50%	0.50%
London Interbank Offered Rate (LIBOR) \| Senior Revolving Credit Facility Maturing in 2023
Debt Instrument [Line Items]
Interest rate margin, percentage				1.00%	1.00%
Minimum \| Senior Revolving Credit Facility Maturing in 2023
Debt Instrument [Line Items]
Interest rate margin, percentage				0.00%	0.00%
Maximum \| Senior Revolving Credit Facility Maturing in 2023
Debt Instrument [Line Items]
Interest rate margin, percentage				175.00%	175.00%