Long-term Debt - Senior Notes (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Cash paid for interest	$ 300	$ 470
Senior Notes [Member] \| 4.875% Senior Unsecured Notes Due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 300,000
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Debt Instrument, Maturity Date	Oct. 15, 2025
Debt Instrument, Date of First Required Payment	Apr. 15, 2018
Senior Notes [Member] \| 4.875% Senior Unsecured Notes Due 2025 [Member] \| Prior to October 15, 2020 [Member]
Debt Instrument [Line Items]
Percentage of principal that can be redeemed with cash from proceeds of an equity offering	35.00%
Debt instrument redemption price with net proceeds from equity offering	104.875%
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes [Member] \| 4.875% Senior Unsecured Notes Due 2025 [Member] \| October 15, 2020 to October 14, 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	102.438%
Senior Notes [Member] \| 4.875% Senior Unsecured Notes Due 2025 [Member] \| October 15, 2021 to October 14, 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	101.219%
Senior Notes [Member] \| 4.875% Senior Unsecured Notes Due 2025 [Member] \| October 15, 2022 and thereafter [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%

Debt instrument redemption price with net cash proceeds of one or more equity offerings

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Percentage of principal amount that can be redeemed with cash proceeds from an equity offering

+ References

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- Definition

Date the debt agreement requires the first payment to be made, in CCYY-MM-DD format.

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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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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

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