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Compensation Plans (Tables) | 12 Months Ended
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Dec. 31, 2018
Compensation Related Costs [Abstract] |  |
Schedule of performance share awards under equity incentive compensation plan [Table Text Block] | A summary of the status and activity of non-vested PSUs is presented in the following table:
| For the Years Ended December 31,
| 2018 |  | 2017 |  | 2016
| PSUs (1) |  | Weighted-Average Grant-Date Fair Value |  | PSUs (1) |  | Weighted-Average Grant-Date Fair Value |  | PSUs (1) |  | Weighted-Average Grant-Date Fair Value
Non-vested at beginning of year | 1,533,491 |  |  | $ | 22.97 |  |  | 828,923 |  |  | $ | 43.25 |  |  | 626,328 |  |  | $ | 61.81 |
Granted | 572,924 |  |  | $ | 24.45 |  |  | 977,731 |  |  | $ | 15.86 |  |  | 447,971 |  |  | $ | 26.56 |
Vested | (233,102 | ) |  | $ | 44.25 |  |  | (94,338 | ) |  | $ | 85.85 |  |  | (130,353 | ) |  | $ | 64.17 |
Forfeited | (162,054 | ) |  | $ | 21.79 |  |  | (178,825 | ) |  | $ | 44.99 |  |  | (115,023 | ) |  | $ | 55.59 |
Non-vested at end of year | 1,711,259 |  |  | $ | 20.68 |  |  | 1,533,491 |  |  | $ | 22.97 |  |  | 828,923 |  |  | $ | 43.25 |
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(1) | The number of awards assumes a multiplier of one. The final number of shares of common stock issued may vary depending on the three-year performance multiplier, which ranges from zero to two.
| [1]
Schedule of shares settled, performance share units [Table Text Block] | A summary of the shares of common stock issued to settle PSUs for the year ended December 31, 2016, is presented in the table below:
| For the Year Ended December 31, 2016
Shares of common stock issued to settle PSUs (1) | 44,870 |
Less: shares of common stock withheld for income and payroll taxes | (14,809 | )
Net shares of common stock issued | 30,061 |
Multiplier earned | 0.2 |
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(1) | During the year ended December 31, 2016, the Company issued shares of common stock to settle PSUs that related to awards granted in 2013. The Company and a majority of grant recipients mutually agreed to net share settle a portion of the awards to cover income and payroll tax withholdings in accordance with the Company’s Equity Plan and individual award agreements.
Schedule of share-based compensation, restricted stock units award activity [Table Text Block] | A summary of the status and activity of non-vested RSUs granted to employees is presented in the following table:
| For the Years Ended December 31,
| 2018 |  | 2017 |  | 2016
| RSUs |  | Weighted- Average Grant-Date Fair Value |  | RSUs |  | Weighted- Average Grant-Date Fair Value |  | RSUs |  | Weighted- Average Grant-Date Fair Value
Non-vested at beginning of year | 1,244,262 |  |  | $ | 20.25 |  |  | 604,116 |  |  | $ | 37.39 |  |  | 543,737 |  |  | $ | 55.01 |
Granted | 583,552 |  |  | $ | 25.77 |  |  | 1,020,780 |  |  | $ | 16.64 |  |  | 417,065 |  |  | $ | 28.08 |
Vested | (407,529 | ) |  | $ | 24.30 |  |  | (246,025 | ) |  | $ | 43.99 |  |  | (241,363 | ) |  | $ | 58.06 |
Forfeited | (177,122 | ) |  | $ | 17.26 |  |  | (134,609 | ) |  | $ | 26.38 |  |  | (115,323 | ) |  | $ | 43.52 |
Non-vested at end of year | 1,243,163 |  |  | $ | 21.50 |  |  | 1,244,262 |  |  | $ | 20.25 |  |  | 604,116 |  |  | $ | 37.39 |
Schedule of shares settled, restricted stock units [Table Text Block] | A summary of the shares of common stock issued to settle employee RSUs is presented in the table below:
| For the Years Ended December 31,
| 2018 |  | 2017 |  | 2016
Shares of common stock issued to settle RSUs (1) | 407,529 |  |  | 246,025 |  |  | 241,363 |
Less: shares of common stock withheld for income and payroll taxes | (115,784 | ) |  | (74,747 | ) |  | (72,181 | )
Net shares of common stock issued | 291,745 |  |  | 171,278 |  |  | 169,182 |
____________________________________________
(1) | During the years ended December 31, 2018, 2017, and 2016, the Company issued shares of common stock to settle RSUs that related to awards granted in previous years. The Company and a majority of grant recipients mutually agreed to net share settle a portion of the awards to cover income and payroll tax withholdings in accordance with the Company’s Equity Plan and individual award agreements.
Schedule of employee stock purchase plan [Table Text Block] | The fair value of ESPP shares issued during the periods reported were estimated using the following weighted-average assumptions:
| For the Years Ended December 31,
| 2018 |  | 2017 |  | 2016
Risk free interest rate | 1.8 | % |  | 0.9 | % |  | 0.4 | %
Dividend yield | 0.4 | % |  | 0.5 | % |  | 0.4 | %
Volatility factor of the expected market price of the Company’s common stock | 55.9 | % |  | 62.5 | % |  | 95.0 | %
Expected life (in years) | 0.5 |  |  | 0.5 |  |  | 0.5 |
Schedule of net profits plan cash payment allocation [Table Text Block] | The following table presents cash payments made or accrued under the Net Profits Plan related to periodic operations, of which the majority is recorded as general and administrative expense, and cash payments made or accrued as a result of divestitures of properties subject to the Net Profits Plan, which are recorded as a reduction to the net gain (loss) on divestiture activity line item in the accompanying statements of operations.
| For the Years Ended December 31,
| 2018 |  | 2017 |  | 2016
| (in thousands)
Cash payments made or accrued related to operations | $ | 63 |  |  | $ | (54 | ) |  | $ | 6,608 |
Cash payments made or accrued related to divestitures | — |  |  | 2,753 |  |  | 24,349 |
Total net settlements | $ | 63 |  |  | $ | 2,699 |  |  | $ | 30,957 |
[1] | (1) The number of awards assumes a multiplier of one. The final number of shares of common stock issued may vary depending on the three-year performance multiplier, which ranges from zero to two.

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- Definition Tabular disclosure of total net settlements made or accrued under the Net Profits Plan, made up of cash payments made or accrued under the Net Profits Plan related to periodic operations, and cash payments made or accrued as a result of divestitures of properties subject to the Net Profits Plan. [Table Text Block] + References No definition available. + Details
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- Definition Tabular disclosure of the number of shares of common stock issued to settle Performance Share Units, net of shares of common stock withheld for income and payroll taxes, and the Performance Share Unit multiplier earned for the year. [Table Text Block] + References No definition available. + Details
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- Definition Tabular disclosure of the number of shares of common stock issued to settle restricted Stock Units, net of shares of common stock withheld for income. [Table Text Block] + References No definition available. + Details
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- Definition Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of employee stock purchase plans, including, but not limited to: (a) expected term, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of number and weighted-average grant date fair value for nonvested performance shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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