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Stock Award Plans and Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended | 92 Months Ended |
--- | --- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2019 | May 02, 2012
Stock-Based Compensation |  |  |  |  |
Common stock, par value (in dollars per share) | $ 0.001 | $ 0.001 |  | $ 0.001 |
Stock-Based Compensation Expense |  |  |  |  |
Forfeiture rate (as a percent) | 5.00% | 5.00% | 5.00% |  |
Stock-based compensation expense | $ 8,200 | $ 7,800 | $ 5,700 |  |
Tax deductions in excess of recognized compensation cost | 7,300 |  |  |  |
Tax benefit | $ 1,500 |  |  |  |
Options |  |  |  |  |
Granted (in shares) | 0 | 0 | 0 |  |
Shares/units |  |  |  |  |
Outstanding at the beginning of the period (in shares) | 820,000 |  |  |  |
Granted (in shares) | 681,000 |  |  |  |
Vested (in shares) | (343,000) |  |  |  |
Forfeited (in shares) | (36,000) |  |  |  |
Outstanding at the end of the period (in shares) | 1,122,000 | 820,000 |  | 1,122,000 |
Weighted-Average Grant Date Fair Value per Share |  |  |  |  |
Outstanding at the beginning of the period (in dollars per share) | $ 18.76 |  |  |  |
Granted (in dollars per share) | 17.08 |  |  |  |
Vested (in dollars per share) | 17.42 |  |  |  |
Forfeited (in dollars per share) | 18.79 |  |  |  |
Outstanding at the end of the period (in dollars per share) | $ 18.15 | $ 18.76 |  | $ 18.15 |
Common Stock |  |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |
Number of shares purchased under the plan | 54,000 | 55,000 | 34,000 |  |
Options |  |  |  |  |
Exercised (in shares) | (775,000) | (273,000) | (2,358,000) |  |
Employee stock purchase plan |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Number of shares of common stock available for future grant | 200,000 |  |  | 200,000 |
Employee Stock Purchase Plan |  |  |  |  |
Purchase price as a percentage of the market value of a common stock on the day the stock is purchased | 85.00% |  |  |  |
Offering period over which compensation expense is amortized | 6 months |  |  |  |
Stock-Based Compensation Expense |  |  |  |  |
Stock-based compensation expense | $ 200 | $ 200 | $ 100 |  |
Employee stock purchase plan | Maximum |  |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |
Payroll deductions as a percentage of employee's salary | 10.00% |  |  |  |
Number of shares purchased under the plan | 100,000 | 100,000 | 100,000 |  |
Restricted Stock Units and Restricted Stock |  |  |  |  |
Weighted-Average Grant Date Fair Value per Share |  |  |  |  |
Granted (in dollars per share) |  | $ 22.41 | $ 20.72 |  |
Restricted Stock Units and Restricted Stock | Employees |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Vesting period | 4 years |  |  |  |
Restricted Stock Units and Restricted Stock | Non-employee members of Board of Directors |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Vesting period | 6 months |  |  |  |
Stock Options |  |  |  |  |
Options |  |  |  |  |
Outstanding at the beginning of the period (in shares) | 2,285,000 |  |  |  |
Exercised (in shares) | (775,000) |  |  |  |
Canceled (in shares) | (1,000) |  |  |  |
Expired (in shares) | (3,000) |  |  |  |
Outstanding at the end of the period (in shares) | 1,506,000 | 2,285,000 |  | 1,506,000 |
Exercisable (in shares) | 1,496,000 |  |  | 1,496,000 |
Options Vested or Expected to Vest at the end of the period (in shares) | 1,506,000 |  |  | 1,506,000 |
Weighted Average Exercise Price |  |  |  |  |
Outstanding at the beginning of the period (in dollars per share) | $ 8.12 |  |  |  |
Exercised (in dollars per share) | 6.59 |  |  |  |
Canceled (in dollars per share) | 12.04 |  |  |  |
Expired (in dollars per share) | 3.72 |  |  |  |
Outstanding at the end of the period (in dollars per share) | 8.92 | $ 8.12 |  | $ 8.92 |
Exercisable at the end of the period (in dollars per share) | 8.89 |  |  | 8.89 |
Options Vested or Expected to Vest at the end of the period (in dollars per share) | $ 8.91 |  |  | $ 8.91 |
Weighted Average Remaining Contractual Term |  |  |  |  |
Outstanding at the end of the period | 1 year 8 months 1 day |  |  |  |
Exercisable at the end of the period | 1 year 7 months 28 days |  |  |  |
Options Vested or Expected to Vest at the end of the period | 1 year 8 months 9 days |  |  |  |
Aggregate Intrinsic Value |  |  |  |  |
Outstanding at the end of the period (in dollars) | $ 22,856 |  |  | $ 22,856 |
Exercisable at the end of the period (in dollars) | 22,760 |  |  | 22,760 |
Options Vested or Expected to Vest at the end of the period (in dollars) | 22,852 |  |  | 22,852 |
Additional disclosure |  |  |  |  |
Total intrinsic value of options exercised (in dollars) | 10,900 | $ 4,100 | $ 39,700 |  |
Total fair value of stock options vested (in dollars) | 900 | $ 1,900 | $ 3,100 |  |
Total forfeiture adjusted unrecognized compensation cost (in dollars) | $ 100 |  |  | $ 100 |
Weighted-average period over which unrecognized compensation cost is expected to be recognized | 10 months 24 days |  |  |  |
Stock Options | Employees |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Vesting period | 4 years |  |  |  |
Period after termination to exercise awards that were vested | 90 days |  |  |  |
Period after termination to retiring employees to exercise vested awards | 1 year |  |  |  |
Stock Options | Non-employee members of Board of Directors |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Vesting period | 6 months |  |  |  |
Restricted Stock |  |  |  |  |
Shares/units |  |  |  |  |
Granted (in shares) | 0 | 0 | 0 |  |
Vested (in shares) | 0 | 0 | 0 |  |
2000 Stock Plan |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Awards granted (in shares) |  |  |  | 0 |
Number of shares of common stock available for future grant | 0 |  |  | 0 |
2000 Stock Plan | Stock Options |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Expiration period | 10 years |  |  |  |
2012 Equity Incentive Plan |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Number of shares of common stock originally reserved for future grant |  |  |  |  | 9,500,000
Common stock, par value (in dollars per share) |  |  |  |  | $ 0.001
Number of shares of common stock available for future grant | 2,700,000 |  |  | 2,700,000 |
2012 Equity Incentive Plan | Restricted Stock Units and Restricted Stock |  |  |  |  |
Additional disclosure |  |  |  |  |
Total forfeiture adjusted unrecognized compensation cost (in dollars) | $ 14,200 |  |  | $ 14,200 |
Weighted-average period over which unrecognized compensation cost is expected to be recognized | 2 years 7 months 6 days |  |  |  |
2012 Equity Incentive Plan | Stock Options |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Expiration period | 7 years |  |  |  |
2012 Equity Incentive Plan | Restricted Stock |  |  |  |  |
Shares/units |  |  |  |  |
Granted (in shares) | 0 | 0 | 0 |  |

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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + 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)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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