Derivative Instruments and Fair Value Measurements - Nonrecurring Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-cash impairment loss	$ 0	$ 0	$ 3,505
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-cash impairment loss			6,005
Fair Value, Measurements, Nonrecurring | AREC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			425
Non-cash impairment loss			3,505
Fair Value, Measurements, Nonrecurring | VestaCare, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			0
Non-cash impairment loss			2,500
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) | AREC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			0
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) | VestaCare, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 2) | AREC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			425
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 2) | VestaCare, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | AREC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | VestaCare, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments			$ 0