Stock-Based Compensation	6 Months Ended
Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The Company has several types of stock-based compensation - stock options, restricted stock, and restricted stock units (“RSUs”) - which are described in note 13 of notes to consolidated financial statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2017. The expense related to stock options and time vested restricted stock is generally fixed. The expense related to RSUs generally fluctuates from period to period dependent, in part, on the Company's absolute stock price and stock price performance relative to its peers. The Company recorded stock-based compensation expense, net of forfeitures, of $3.4 million and $2.9 million for the three months ended June 30, 2018 and 2017, respectively, and $6.0 million and $4.6 million for the six months ended June 30, 2018 and 2017, respectively. The Company maintains the 2009 Incentive Stock Plan (the "2009 Plan") and the 2005 Restricted Stock Unit Plan (the “RSU Plan”). Under the 2009 Plan, during the quarter ended March 31, 2018, the Company made restricted stock grants of 315,199 shares to key employees, which vest ratably over a three-year period. Under the RSU Plan, during the quarter ended March 31, 2018, the Company awarded two types of performance-based RSUs to key employees based on the following metrics: (1) Total Stockholder Return of the Company, as defined in the RSU Plan, as compared to the companies in the SNL US REIT Office index (“TSR RSUs”) and (2) the ratio of cumulative funds from operations per share to targeted cumulative funds from operations per share (“FFO RSUs”) as defined in the RSU Plan. The performance period for both awards is January 1, 2018 to December 31, 2020, and the targeted units awarded of TSR RSUs and FFO RSUs was 315,124 and 135,054, respectively. The ultimate payout of these awards can range from 0% to 200% of the targeted number of units depending on the achievement of the market and performance metrics described above. These RSU awards cliff vest on December 31, 2020 and are to be settled in cash with payment dependent upon attainment of required service, market, and performance criteria. The number of RSUs vesting will be determined by the Compensation Committee, and the payout per unit will be equal to the average closing price on each trading day during the 30-day period ending on December 31, 2020. The Company expenses an estimate of the fair value of the TSR RSUs over the performance period using a quarterly Monte Carlo valuation. The FFO RSUs are expensed over the vesting period using the fair market value of the Company's stock at the reporting date multiplied by the anticipated number of units to be paid based on the current estimate of what the ratio is expected to be upon vesting. Dividend equivalents on the TSR RSUs and the FFO RSUs will also be paid based upon the percentage vested. During the quarter ended June 30, 2018, the Company issued 118,555 shares of common stock at fair value to members of its board of directors in lieu of fees, and recorded $1.1 million in general and administrative expense related to these issuances. During the quarter ended June 30, 2018, 457,206 stock options were exercised. As a result, the Company issued 47,309 shares and paid $945,000 to optionees.

STOCK-BASED COMPENSATION

The Company has several types of stock-based compensation - stock options, restricted stock, and restricted stock units (“RSUs”) - which are described in note 13 of notes to consolidated financial statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2017. The expense related to stock options and time vested restricted stock is generally fixed. The expense related to RSUs generally fluctuates from period to period dependent, in part, on the Company's absolute stock price and stock price performance relative to its peers. The Company recorded stock-based compensation expense, net of forfeitures, of $3.4 million and $2.9 million for the three months ended June 30, 2018 and 2017, respectively, and $6.0 million and $4.6 million for the six months ended June 30, 2018 and 2017, respectively.

The Company maintains the 2009 Incentive Stock Plan (the "2009 Plan") and the 2005 Restricted Stock Unit Plan (the “RSU Plan”). Under the 2009 Plan, during the quarter ended March 31, 2018, the Company made restricted stock grants of 315,199 shares to key employees, which vest ratably over a three-year period. Under the RSU Plan, during the quarter ended March 31, 2018, the Company awarded two types of performance-based RSUs to key employees based on the following metrics: (1) Total Stockholder Return of the Company, as defined in the RSU Plan, as compared to the companies in the SNL US REIT Office index (“TSR RSUs”) and (2) the ratio of cumulative funds from operations per share to targeted cumulative funds from operations per share (“FFO RSUs”) as defined in the RSU Plan. The performance period for both awards is January 1, 2018 to December 31, 2020, and the targeted units awarded of TSR RSUs and FFO RSUs was 315,124 and 135,054, respectively. The ultimate payout of these awards can range from 0% to 200% of the targeted number of units depending on the achievement of the market and performance metrics described above. These RSU awards cliff vest on December 31, 2020 and are to be settled in cash with payment dependent upon attainment of required service, market, and performance criteria. The number of RSUs vesting will be determined by the Compensation Committee, and the payout per unit will be equal to the average closing price on each trading day during the 30-day period ending on December 31, 2020. The Company expenses an estimate of the fair value of the TSR RSUs over the performance period using a quarterly Monte Carlo valuation. The FFO RSUs are expensed over the vesting period using the fair market value of the Company's stock at the reporting date multiplied by the anticipated number of units to be paid based on the current estimate of what the ratio is expected to be upon vesting. Dividend equivalents on the TSR RSUs and the FFO RSUs will also be paid based upon the percentage vested.

During the quarter ended June 30, 2018, the Company issued 118,555 shares of common stock at fair value to members of its board of directors in lieu of fees, and recorded $1.1 million in general and administrative expense related to these issuances.

During the quarter ended June 30, 2018, 457,206 stock options were exercised. As a result, the Company issued 47,309 shares and paid $945,000 to optionees.