Long Term Debt (Schedule of Long Term Debt) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,340,631	$ 1,298,783
Less unamortized discount	3,197	3,518
Less unamortized deferred loan fees	14,117	15,133
Less current portion of long-term debt	2,989	3,326
Long-term debt, net	$ 1,320,328	1,276,806
Minimum
Debt Instrument [Line Items]
Interest coverage ratio	2.50
Maximum
Debt Instrument [Line Items]
Total leverage ratio	5.95
Senior leverage ratio	3.00
Medium-term Notes \| Senior Credit Facility \| Term Loan B
Debt Instrument [Line Items]
Principal payments (as a percent)	0.25%
Long-term debt, gross	$ 242,583	245,187
Medium-term Notes \| Senior Credit Facility \| Term Loan B \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.25%
Medium-term Notes \| Senior Credit Facility \| Term Loan A
Debt Instrument [Line Items]
Long-term debt, gross	$ 215,000	215,000
Medium-term Notes \| Senior Credit Facility \| Term Loan A \| Minimum \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.00%
Medium-term Notes \| Senior Credit Facility \| Term Loan A \| Maximum \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.00%
Line of Credit \| Revolving Credit Facility \| Maximum
Debt Instrument [Line Items]
Senior leverage ratio	3.00
Line of Credit \| Senior Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000	55,000
Line of Credit \| Senior Credit Facility \| Revolving Credit Facility \| Minimum \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.00%
Line of Credit \| Senior Credit Facility \| Revolving Credit Facility \| Maximum \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.00%
Senior Notes \| 2025 Notes
Debt Instrument [Line Items]
Stated percentage	6.875%
Long-term debt, gross	$ 450,000	450,000
Senior Notes \| 2021 Notes
Debt Instrument [Line Items]
Stated percentage	6.75%
Long-term debt, gross	$ 325,000	325,000
Notes Payable to Banks \| Wells Fargo Note
Debt Instrument [Line Items]
Long-term debt, gross	$ 8,048	$ 8,596
Notes Payable to Banks \| Wells Fargo Note \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.25%

Percentage of principal used to calculate annual principal payment.

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- Definition

Senior Credit Facility, Interest Coverage Ratio

+ References

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- Definition

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

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

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

+ References

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- Definition

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.

+ References

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- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

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-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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

+ References

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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