Stockholders' Equity	12 Months Ended
Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock. The Company’s certificate of incorporation, as amended, authorizes the issuance of up to five million preferred shares. The Board of Directors is authorized to fix the number of shares of any series of preferred stock and to determine the designation of such shares. However, the amended certificate of incorporation specifies the initial series and the rights of that series. No shares of preferred stock were outstanding as of December 31, 2017, 2016 or 2015. Equity Incentive Plan. The Company grants stock options, time-based restricted stock units ("RSUs") and performance-based restricted stock units ("PSUs") to employees and non-employee directors under its 2016 Equity Incentive Plan (the “2016 Plan”). The Company previously granted stock options under the Amended and Restated 2010 Equity Incentive Plan (the "2010 Plan") and the Amended and Restated 2001 Equity Incentive Plan (the "2001 Plan"). The 2010 Plan and 2001 Plan were terminated at the time of adoption of the 2016 Plan, but the terminated Plans continue to govern outstanding options granted thereunder. The Company has stock options, RSUs and PSUs outstanding, which were issued under each of these equity incentive plans to certain employees and directors. Stock options granted under these plans have terms ranging up to ten years, have exercise prices ranging from $8.50 to $41.36 per share, and generally vest over four years. As of December 31, 2017, approximately 1.8 million shares remained available for grant under the 2016 Plan. Restricted Stock Units. The Company grants both RSUs and PSUs to certain officers, directors and management. Until the restrictions lapse, ownership of the affected restricted stock units granted to the Company’s officers, directors and management is conditional upon continuous employment with the Company. For the years ended December 31, 2017, 2016 and 2015, the Company granted approximately 0.3 million, 0.2 million and 0.2 million shares, respectively, of restricted stock units to officers and management, which either have a time-based four-year vesting provision or performance-based vesting provisions. For purposes of measuring compensation expense of PSUs, the amount of shares ultimately expected to vest is estimated at each reporting date based on management’s expectations regarding the relevant performance criteria. The grant date of the PSUs takes place when the grant is authorized and the specific achievement goals are communicated. The recognition of compensation expense associated with the PSUs requires judgment in assessing the probability of meeting the performance goals. This may result in significant expense recognition in the period in which the performance goals are met or when achievement of the goals is deemed probable or may result in the reversal of previously recognized stock-based compensation expense if the performance criteria are deemed not probable of being met. During the year ended December 31, 2017, common stock was issued to certain members of the Board of Directors in lieu of cash compensation for these members that elected to participate and agree to hold the stock for the elected deferral period. During the years ended December 31, 2016 and 2015, RSUs were granted to certain members of the Board of Directors in lieu of cash compensation as a part of the Company’s non-employee director’s deferred compensation program. The compensation expense associated with these RSU grants were $0.1 million, $0.4 million and $0.5 million for the years ended December 31, 2017, 2016 and 2015, respectively. Employee Deferred Bonus Compensation Program. For the year ended December 31, 2017, the deferred bonus compensation program was suspended temporarily by the Board. For the years ended December 31, 2016 and 2015, certain employees of the Company were eligible to participate in the Company’s deferred bonus compensation program with respect to any payments received under the Company’s cash incentive plan. Participating employees could elect to receive 50% or 100% of the cash value of their cash bonus in the form of fully vested, restricted stock units plus an additional premium as additional restricted stock units, issued under the 2016 Plan. The premium restricted stock units are subject to a one-year vesting requirement from the date of issuance. The additional premium will be determined based on the length of time of the deferral period selected by the participating employee as follows: (i) if one year from the date of grant, a premium of 10% on the amount deferred, (ii) if two years from the date of grant, a premium of 20% on the amount deferred, or (iii) if four years from the date of grant, a premium of 30% on the amount deferred. Employee Stock Purchase Plan. Under the Company’s Amended and Restated 1983 Employee Stock Purchase Plan (the “ESPP”), full-time employees are allowed to purchase common stock through payroll deductions (which cannot exceed 10% of the employee’s compensation) at the lower of 85% of fair market value at the beginning or end of each six-month purchase period. As of December 31, 2017, 1,272,274 shares had been sold under the Plan, leaving 227,726 shares available for future issuance. Share Repurchase Program. On January 25, 2016, the Company's Board of Directors authorized an amendment to extend the previously announced stock repurchase program. The Board of Directors has authorized the Company to repurchase up to an aggregate of $50.0 million in shares of our common stock under our stock repurchase program. Any shares of common stock repurchased under this program will no longer be deemed outstanding upon repurchase and will be returned to the pool of authorized shares. During the year ended December 31, 2016, 1,152,386 shares of outstanding common stock were repurchased under the Company's previously announced share repurchase program for approximately $19.6 million. During the year ended December 31, 2015, 1,397,000 shares of outstanding common stock were repurchased under the Company's previously announced share repurchase program for approximately $30.4 million. There were no repurchases during 2017 and at December 31, 2017, $35.0 million remained available under this program. The repurchase program expired on January 25, 2018. Shares Reserved for Future Issuance. At December 31, 2017, approximately 5.3 million shares of common stock were reserved under the Company’s equity incentive plan and 227,726 shares were reserved for purchases under the ESPP.

Stockholders’ Equity

Preferred Stock. The Company’s certificate of incorporation, as amended, authorizes the issuance of up to five million preferred shares. The Board of Directors is authorized to fix the number of shares of any series of preferred stock and to determine the designation of such shares. However, the amended certificate of incorporation specifies the initial series and the rights of that series. No shares of preferred stock were outstanding as of December 31, 2017, 2016 or 2015.

Equity Incentive Plan. The Company grants stock options, time-based restricted stock units ("RSUs") and performance-based restricted stock units ("PSUs") to employees and non-employee directors under its 2016 Equity Incentive Plan (the “2016 Plan”). The Company previously granted stock options under the Amended and Restated 2010 Equity Incentive Plan (the "2010 Plan") and the Amended and Restated 2001 Equity Incentive Plan (the "2001 Plan"). The 2010 Plan and 2001 Plan were terminated at the time of adoption of the 2016 Plan, but the terminated Plans continue to govern outstanding options granted thereunder. The Company has stock options, RSUs and PSUs outstanding, which were issued under each of these equity incentive plans to certain employees and directors. Stock options granted under these plans have terms ranging up to ten years, have exercise prices ranging from $8.50 to $41.36 per share, and generally vest over four years. As of December 31, 2017, approximately 1.8 million shares remained available for grant under the 2016 Plan.

Restricted Stock Units. The Company grants both RSUs and PSUs to certain officers, directors and management. Until the restrictions lapse, ownership of the affected restricted stock units granted to the Company’s officers, directors and management is conditional upon continuous employment with the Company.

For the years ended December 31, 2017, 2016 and 2015, the Company granted approximately 0.3 million, 0.2 million and 0.2 million shares, respectively, of restricted stock units to officers and management, which either have a time-based four-year vesting provision or performance-based vesting provisions. For purposes of measuring compensation expense of PSUs, the amount of shares ultimately expected to vest is estimated at each reporting date based on management’s expectations regarding the relevant performance criteria. The grant date of the PSUs takes place when the grant is authorized and the specific achievement goals are communicated. The recognition of compensation expense associated with the PSUs requires judgment in assessing the probability of meeting the performance goals. This may result in significant expense recognition in the period in which the performance goals are met or when achievement of the goals is deemed probable or may result in the reversal of previously recognized stock-based compensation expense if the performance criteria are deemed not probable of being met.

During the year ended December 31, 2017, common stock was issued to certain members of the Board of Directors in lieu of cash compensation for these members that elected to participate and agree to hold the stock for the elected deferral period. During the years ended December 31, 2016 and 2015, RSUs were granted to certain members of the Board of Directors in lieu of cash compensation as a part of the Company’s non-employee director’s deferred compensation program. The compensation expense associated with these RSU grants were $0.1 million, $0.4 million and $0.5 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Employee Deferred Bonus Compensation Program. For the year ended December 31, 2017, the deferred bonus compensation program was suspended temporarily by the Board. For the years ended December 31, 2016 and 2015, certain employees of the Company were eligible to participate in the Company’s deferred bonus compensation program with respect to any payments received under the Company’s cash incentive plan. Participating employees could elect to receive 50% or 100% of the cash value of their cash bonus in the form of fully vested, restricted stock units plus an additional premium as additional restricted stock units, issued under the 2016 Plan. The premium restricted stock units are subject to a one-year vesting requirement from the date of issuance. The additional premium will be determined based on the length of time of the deferral period selected by the participating employee as follows: (i) if one year from the date of grant, a premium of 10% on the amount deferred, (ii) if two years from the date of grant, a premium of 20% on the amount deferred, or (iii) if four years from the date of grant, a premium of 30% on the amount deferred.

Employee Stock Purchase Plan. Under the Company’s Amended and Restated 1983 Employee Stock Purchase Plan (the “ESPP”), full-time employees are allowed to purchase common stock through payroll deductions (which cannot exceed 10% of the employee’s compensation) at the lower of 85% of fair market value at the beginning or end of each six-month purchase period. As of December 31, 2017, 1,272,274 shares had been sold under the Plan, leaving 227,726 shares available for future issuance.

Share Repurchase Program. On January 25, 2016, the Company's Board of Directors authorized an amendment to extend the previously announced stock repurchase program. The Board of Directors has authorized the Company to repurchase up to an aggregate of $50.0 million in shares of our common stock under our stock repurchase program. Any shares of common stock repurchased under this program will no longer be deemed outstanding upon repurchase and will be returned to the pool of authorized shares. During the year ended December 31, 2016, 1,152,386 shares of outstanding common stock were repurchased under the Company's previously announced share repurchase program for approximately $19.6 million. During the year ended December 31, 2015, 1,397,000 shares of outstanding common stock were repurchased under the Company's previously announced share repurchase program for approximately $30.4 million. There were no repurchases during 2017 and at December 31, 2017, $35.0 million remained available under this program. The repurchase program expired on January 25, 2018.

Shares Reserved for Future Issuance. At December 31, 2017, approximately 5.3 million shares of common stock were reserved under the Company’s equity incentive plan and 227,726 shares were reserved for purchases under the ESPP.