Fair Value of Financial Instruments - Schedule of Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial liabilities:
Notes payable	$ 185,817	$ 175,181
Notes payable, fair value	185,817	175,181
Subordinated amortizing notes
Financial liabilities:
Total senior notes	12,390	14,066
Long-term Debt, Fair Value	9,514,033	12,122
5 3/4% Senior Notes due April 15, 2019
Financial liabilities:
Total senior notes	148,429	148,295
Long-term Debt, Fair Value	$ 143,250	$ 147,750
Stated interest rate	5.75%	5.75%
8 1/2% Senior Notes due November 15, 2020
Financial liabilities:
Total senior notes	$ 422,887	$ 422,896
Long-term Debt, Fair Value	$ 434,563	$ 449,438
Stated interest rate	8.50%	8.50%
7% Senior Notes due August 15, 2022
Financial liabilities:
Total senior notes	$ 345,474	$ 345,338
Long-term Debt, Fair Value	$ 334,250	$ 350,875
Stated interest rate	7.00%	7.00%
Carrying Amount
Financial liabilities:
Notes payable	$ 185,817	$ 175,181
Total senior notes	1,114,997	1,105,776
Carrying Amount | Subordinated amortizing notes
Financial liabilities:
Total senior notes	12,390	14,066
Carrying Amount | 5 3/4% Senior Notes due April 15, 2019
Financial liabilities:
Total senior notes	148,429	148,295
Carrying Amount | 8 1/2% Senior Notes due November 15, 2020
Financial liabilities:
Total senior notes	422,887	422,896
Carrying Amount | 7% Senior Notes due August 15, 2022
Financial liabilities:
Total senior notes	$ 345,474	$ 345,338