Fair Value of Financial Instruments - Schedule of Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial liabilities:
Notes payable, fair value	$ 172,246	$ 94,515
5 3/4% Senior Notes due April 15, 2019
Financial liabilities:
Long-term debt, fair value	$ 0	$ 151,500
Stated interest rate	5.75%	5.75%
7% Senior Notes due August 15, 2022
Financial liabilities:
Long-term debt, fair value	$ 359,625	$ 362,250
Stated interest rate	7.00%	7.00%
6% Senior Notes due 2023
Financial liabilities:
Long-term debt, fair value	$ 349,125	$ 0
Stated interest rate	6.00%
5 7/8% Senior Notes due January 31, 2025
Financial liabilities:
Long-term debt, fair value	$ 436,500	459,000
Stated interest rate	5.875%
Carrying Amount
Financial liabilities:
Notes payable, fair value	$ 172,246	94,515
Carrying Amount | 5 3/4% Senior Notes due April 15, 2019
Financial liabilities:
Long-term debt, fair value	0	149,362
Carrying Amount | 7% Senior Notes due August 15, 2022
Financial liabilities:
Long-term debt, fair value	346,924	346,740
Carrying Amount | 6% Senior Notes due 2023
Financial liabilities:
Long-term debt, fair value	343,274	0
Carrying Amount | 5 7/8% Senior Notes due January 31, 2025
Financial liabilities:
Long-term debt, fair value	$ 439,903	$ 439,567