Stock Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Based Compensation

We are authorized to issue up to 10.6 million shares of the General Partner's common stock under our stock-based employee and non-employee compensation plans.

Restricted Stock Units ("RSUs")

Under our 2015 Long-Term Incentive Plan, which was approved by the General Partner's shareholders in April 2015, and our 2015 Non-Employee Directors Compensation Plan (collectively, the "Compensation Plans"), RSUs may be granted to non-employee directors, executive officers and selected employees. A RSU is economically equivalent to a share of the General Partner's common stock and RSUs are valued based on the market price of the General Partner's common stock on the date of the award.

RSUs granted to employees from 2015 to 2019 vest ratably in most cases over a three-year period, and are payable in shares of our common stock with a new share of such common stock issued upon each RSU's vesting. RSUs granted to employees prior to 2015 vest ratably over a five-year period and are payable in the same manner. RSUs granted to existing non-employee directors vest 100% over one year and have contractual lives of one year.

To the extent that a recipient of a RSU grant is not determined to be retirement eligible, as defined by the Compensation Plans, we recognize expense on a straight-line basis over the vesting period. Expense is recognized immediately at the date of grant to the extent a recipient is retirement eligible and expense is accelerated to the extent that a participant will become retirement eligible prior to the end of the contractual life of granted RSUs.

The following table summarizes transactions for our RSUs, excluding dividend equivalents, for 2019: 

Restricted Stock Units	Number of RSUs		Weighted Average Grant-Date Fair Value
RSUs at December 31, 2018	956,403		$23.36
Granted	392,345		$29.98
Vested	(590,364	)	$22.15
Forfeited	(10,204	)	$27.60
RSUs at December 31, 2019	748,180		$27.73

Compensation cost recognized for RSUs totaled $11.0 million, $11.9 million and $11.2 million for the years ended December 31, 2019, 2018 and 2017, respectively.

As of December 31, 2019, there was $6.0 million of total unrecognized compensation expense related to nonvested RSUs granted under the Plan, which is expected to be recognized over a weighted average period of 1.7 years.

The total intrinsic value (which is equal to the value of a share of the General Partner's common stock on the date of vesting) of RSUs vested during the years ended December 31, 2019, 2018 and 2017 was $17.7 million, $18.3 million and $19.3 million, respectively.

The weighted average grant-date fair value of RSUs granted during 2018 and 2017 was $25.38 and $25.42, respectively.

The weighted average grant-date fair value of nonvested RSUs as of December 31, 2017 was $20.79.