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Long-Term Debt - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	May 30, 2017
Debt Instrument [Line Items]
Total long-term debt	$ 636,394	$ 590,887	$ 600,722
Deferred finance costs, net	3,600	4,100	4,300
Revolving unsecured credit facility, maturing 2023 (1) \| Line of Credit
Debt Instrument [Line Items]
Total long-term debt	340,000	295,000	305,000
5.375% senior unsecured notes due 2024 \| Senior Notes
Debt Instrument [Line Items]
Total long-term debt	$ 296,394	$ 295,887	$ 295,722
Stated interest rate (as a percent)	5.375%			5.375%