Equity Incentive Awards (Tables)

12 Months Ended

Dec. 31, 2019

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, 2016	131,214		$31.84
Shares granted	260,852		$38.13
Shares forfeited	(1,980	)	$40.27
Shares vested	(250,542	)	$34.40
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

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:                

	2018	2017
Dividend Yield	2.5%	2.4%
Risk-free interest rate	2.8%	1.9%
Expected Life	5.6 years	5.5 years
Expected Volatility	16.7%	17.8%
Weighted Average Grant Date Fair Value Per Share	$6.48	$5.50

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, 2016	866,300		$10.72	1.7	$22.0
Options issued	13,860		$40.58
Options exercised	(440,000	)	$11.02		$14.5
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
Exercisable at December 31, 2019	37,782		$40.24	7.2	$1.1