Fair Value of Financial Instruments - Schedule of Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial liabilities:
Notes payable, fair value	$ 290,234	$ 198,019
5 3/4% Senior Notes due April 15, 2019
Financial liabilities:
Stated interest rate	5.75%	5.75%
7% Senior Notes due August 15, 2022
Financial liabilities:
Long-term debt, fair value	$ 351,750	$ 350,000
Stated interest rate	7.00%	7.00%
6% Senior Notes due September 1, 2023
Financial liabilities:
Long-term debt, fair value	$ 357,875	$ 315,000
Stated interest rate	6.00%
5 7/8% Senior Notes due January 31, 2025
Financial liabilities:
Long-term debt, fair value	$ 435,794	$ 378,611
Stated interest rate	5.875%	5.875%
Carrying Amount
Financial liabilities:
Notes payable, fair value	$ 290,234	$ 198,019
Carrying Amount | 7% Senior Notes due August 15, 2022
Financial liabilities:
Long-term debt, fair value	347,821	347,456
Carrying Amount | 6% Senior Notes due September 1, 2023
Financial liabilities:
Long-term debt, fair value	344,526	343,878
Carrying Amount | 5 7/8% Senior Notes due January 31, 2025
Financial liabilities:
Long-term debt, fair value	$ 428,775	$ 431,992