Equity Incentive Award Plan (Tables)

3 Months Ended

Mar. 31, 2020

Equity Incentive Award Plan

Schedule of stock option activity

	Number of
	Shares	Weighted-
	Subject to	Average
	Option	Exercise Price
Options outstanding, December 31, 2019	31,746	$	19.57
Granted	—		—
Exercised	(3,210)		18.87
Forfeited	—		—
Expired	—		—
Options outstanding, March 31, 2020	28,536	$	19.65

Schedule of restricted awards and RSUs

	Restricted	Weighted-
	Stock	Average Fair
	Awards and	Value at Grant
	Units	Date
Unvested balance, December 31, 2019	292,373	$	96.44
Granted	146,582		110.73
Forfeited	(4,913)		99.04
Vested	(112,245)		90.76
Unvested balance, March 31, 2020	321,797	$	104.90

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, 2019	34,624	171,351	102,989	$	107.84
Granted	10,210	71,488	40,852		125.02
Performance adjustment (1)	38,047	(7,904)	15,073		—
Forfeited	(1,049)	(4,878)	(2,964)		107.63
Vested	(32,524)	(32,524)	(32,524)		105.55
Unvested balance, March 31, 2020	49,308	197,533	123,426	$	113.96

(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

	Three Months Ended March 31,
	2020		2019
Expected term (in years)	2.82		2.82
Expected volatility	24.00	%	24.09	%
Expected annual dividend(1)	—		—
Risk-free rate	0.56	%	2.48	%

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