Equity Incentive Awards (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Restricted Stock Activities and Related Information

A summary of our restricted stock activities and related information, as adjusted for stock split, is as follows:

	Number of Shares	Weighted Average Grant Date Fair Value Per Share
Balance at December 31, 2017	139,544	$38.89
Shares granted	385,010	$43.01
Shares vested	(224,852)	$40.74
Balance at December 31, 2018	299,702	$42.78
Shares granted	193,262	$55.51
Shares vested	(74,222)	$43.72
Balance at December 31, 2019	418,742	$48.32
Shares granted	151,104	$56.07
Shares vested	(221,055)	$47.74
Balance at December 31, 2020	348,791	$53.06

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The fair value of stock options granted was estimated on the grant date using the Black-Scholes-Merton model. The following table includes the assumptions made in the valuation, as adjusted for stock split:

	2020	2019	2018
Dividend Yield	2.1%	—%	2.5%
Risk-free interest rate	0.3%	—%	2.8%
Expected Life	5.6 years	0	5.6 years
Expected Volatility	49.2%	—%	16.7%
Weighted Average Grant Date Fair Value Per Share	$29.58	$—	$6.48

Summary of Stock Option Activity

A summary of our stock option activity and related information, as adjusted for stock split, is as follows:

	Shares Subject To Options	Weighted Average Exercise Price Per Share	Weighted Average Outstanding Contractual Life (in years)	Average Intrinsic Value (in millions)
Balance at December 31, 2017	440,160	$11.36	1.6	$14.6
Options issued	12,540	$44.83
Options exercised	(405,600)	$9.43		$16.9
Balance at December 31, 2018	47,100	$36.95	7.3	$0.5
Options exercised	(5,600)	$9.43		$0.2
Balance at December 31, 2019	41,500	$40.65	7.3	$1.2
Options issued	16,090	$66.81
Balance at December 31, 2020	57,590	$47.96	7.2	$0.9
Exercisable at December 31, 2020	41,500	$40.65	6.3	$0.9