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

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- Definition

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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- Definition

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

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

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No definition available.

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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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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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The fair value of notes issued in noncash investing and financing activities.

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Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

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Debt (Narrative) (Details) - USD ($)			1 Months Ended	3 Months Ended
Debt (Narrative) (Details) - USD ($)	Jan. 24, 2019	Dec. 09, 2015	Jan. 31, 2013	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Standby letters of credit					$ 9,200,000
Availability amount					290,800,000	$ 288,800,000
Carrying value of outstanding debt					$ 210,405,000	$ 210,021,000
Senior Subordinated 6.25% Notes
Debt Instrument [Line Items]
Notes issued			$ 210,000,000
Interest rate			6.25%		6.25%	6.25%
Carrying value of outstanding debt					$ 210,000,000	$ 210,000,000
Revolving Credit Facility \| Senior Credit Agreement
Debt Instrument [Line Items]
Current borrowing capacity		$ 300,000,000
Maximum borrowing capacity under the revolving credit facility		$ 500,000,000
Revolving Credit Facility \| Senior Credit Agreement \| Minimum
Debt Instrument [Line Items]
Annual commitment fee		0.20%
Revolving Credit Facility \| Senior Credit Agreement \| Minimum \| LIBOR
Debt Instrument [Line Items]
LIBOR floor, plus		1.25%
Revolving Credit Facility \| Senior Credit Agreement \| Maximum
Debt Instrument [Line Items]
Annual commitment fee		0.30%
Revolving Credit Facility \| Senior Credit Agreement \| Maximum \| LIBOR
Debt Instrument [Line Items]
LIBOR floor, plus		2.25%
Term Loan \| Senior Credit Agreement
Debt Instrument [Line Items]
Term loan (up to)		$ 200,000,000
Subsequent Event \| Revolving Credit Facility \| 2019 Senior Credit Agreement [Member]
Debt Instrument [Line Items]
Current borrowing capacity	$ 400,000,000
Maximum borrowing capacity under the revolving credit facility	$ 700,000,000
Subsequent Event \| Revolving Credit Facility \| 2019 Senior Credit Agreement [Member] \| Minimum
Debt Instrument [Line Items]
Annual commitment fee	0.15%
Subsequent Event \| Revolving Credit Facility \| 2019 Senior Credit Agreement [Member] \| Minimum \| LIBOR
Debt Instrument [Line Items]
LIBOR floor, plus	1.125%
Subsequent Event \| Revolving Credit Facility \| 2019 Senior Credit Agreement [Member] \| Maximum
Debt Instrument [Line Items]
Annual commitment fee	0.25%
Subsequent Event \| Revolving Credit Facility \| 2019 Senior Credit Agreement [Member] \| Maximum \| LIBOR
Debt Instrument [Line Items]
LIBOR floor, plus	2.00%
Subsequent Event \| Term Loan \| 2019 Senior Credit Agreement [Member]
Debt Instrument [Line Items]
Term loan (up to)	$ 300,000,000
Scenario, Forecast \| Senior Subordinated 6.25% Notes
Debt Instrument [Line Items]
Write off of deferred debt issuance cost				$ 1,000,000