Equity Incentive Award Plan (Tables)

6 Months Ended

Jun. 30, 2019

Schedule of stock option activity

	Number of
	Shares	Weighted-
	Subject to	Average
	Option	Exercise Price
Options outstanding, December 31, 2018	49,133	$	20.06
Granted	—		—
Exercised	(2,468)		15.35
Forfeited	—		—
Expired	—		—
Options outstanding, June 30, 2019	46,665	$	20.31

Schedule of restricted awards and RSUs

	Restricted	Weighted-
	Stock	Average Fair
	Awards and	Value at Grant
	Units	Date
Unvested balance, December 31, 2018	284,879	$	85.98
Granted	157,446		100.79
Forfeited	(15,522)		92.22
Vested	(119,002)		79.03
Unvested balance, June 30, 2019	307,801	$	95.93

Schedule of unvested PSAs and their weighted-average fair value at the date of grant

				Weighted-
				Average Fair
	Performance-Based Restricted Stock Awards			Value at Grant
	Minimum	Maximum	Target	Date
Unvested balance, December 31, 2018	50,823	173,944	112,385	$	96.58
Granted	10,926	76,480	43,703		114.55
Performance adjustment (1)	18,063	(29,819)	(5,878)		—
Forfeited	(1,538)	(5,604)	(3,571)		103.26
Vested	(43,650)	(43,650)	(43,650)		84.78
Unvested balance, June 30, 2019	34,624	171,351	102,989	$	107.84

(1) Includes the annual adjustment for the number of PSAs earned based on our achievement of relative TSR measured versus the MSCI US REIT Index for the applicable performance periods.

Summary of assumptions used to value stock option awards

	Six Months Ended June 30,
	2019		2018
Expected term (in years)	2.82		2.82
Expected volatility	24.09	%	24.15	%
Expected annual dividend(1)	—		—
Risk-free rate	2.48	%	2.24	%

(1) The fair value of the PSAs assumes reinvestment of dividends.