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Percent of consolidated net income

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

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

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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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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Face (par) amount of the original debt instrument that was repurchased.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt premium.

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

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The cash outflow for the extinguishment of long-term borrowing, with the highest claim on the assets of the entity in case of bankruptcy or liquidation, before its maturity.

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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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Senior Notes and Unsecured Revolving Credit Facility - Additional Disclosures (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	May 04, 2017	Mar. 17, 2017
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 84,000,000		$ 67,500,000
Long-term Debt	399,591,000		387,648,000
Debt Instrument, Unamortized Discount	1,500,000		1,700,000
Debt Instrument, Unamortized Premium	1,200,000		1,300,000
Debt Instrument, Unamortized Debt Issuance Costs	$ 4,100,000		4,500,000
Interest rate	7.25%
Debt Instrument, Repurchased Face Amount	$ 5,000,000
Percent of Debt Instrument Face Value Repurchased	90.25%
Early Repayment of Senior Debt	$ 4,512,000	$ 0
Gain on early extinguishment of debt	417,000	$ 0
Write off of Deferred Debt Issuance Cost	70,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 200,000,000
Interest rate at period end	5.49%
Revolving Credit Facility [Member] \| Minimum [Member] \| Unsecured Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%
Revolving Credit Facility [Member] \| Maximum [Member] \| Unsecured Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%
Letter of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 25,000,000
Letters of Credit Outstanding, Amount	2,300,000		$ 2,300,000
Accordion Feature Maximum Borrowing Capacity [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 300,000,000
Sr Notes Due 2022 [Member]
Debt Instrument [Line Items]
Face value of note					$ 250,000,000
Interest rate	7.25%
Percent of Debt Instrument Par Value Issued					98.96%
Interest rate at period end					7.50%
Sr Notes Due 2022 Tack-on [Member]
Debt Instrument [Line Items]
Face value of note				$ 75,000,000
Percent of Debt Instrument Par Value Issued				102.75%
Interest rate at period end				6.44%
Existing or future credit facility borrowings [Member] \| Sr Notes Due 2022 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 260,000,000
Basket limitation components [Member] \| Sr Notes Due 2022 [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Percent of consolidated net income	50.00%
Net Cash Proceeds from Qualified Equity Offerings	100.00%
Consolidated tangible net assets	15.00%
General Basket	$ 15,000,000