Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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

Schedule of stock options outstanding by exercise price range

The following summarizes information about stock options outstanding and exercisable at December 31, 2017:

	Options outstanding				Options exercisable
Range of exercise prices per share	Number outstanding	Weighted average exercise price per share		Weighted average contractual term (in years)	Number exercisable	Weighted average exercise price per share		Weighted average contractual term (in years)
$11.09 - 12.80	32,691	$	12.37	2.93	32,691	$	12.37	2.93
$13.20 - 16.24	136,604	15.94		4.92	136,604	15.94		4.92
$19.97 - 21.10	49,546	20.36		2.62	49,546	20.36		2.62
$23.78 - 25.14	232,582	24.56		4.33	232,582	24.56		4.33
$29.45 - 32.81	537,893	31.68		7.62	290,534	30.72		7.15
$46.95 - 53.72	121,602	53.40		9.25	38,091	53.72		9.23
$11.09 - 53.72	1,110,918	$	29.56	6.42	780,048	$	25.99	5.56

Summary of activity for Corporation's stock options

A summary of activity for the Corporation's stock options as of and during the years ended December 31, 2017, 2016 and 2015 is presented below:

	Non-vested stock options outstanding						Stock options outstanding
	Number of options		Weighted- average exercise price per share		Weighted- average grant date fair value per share		Number of options		Weighted- average exercise price per share
Outstanding at December 31, 2014	432,199		$	26.75	$	8.30	1,037,311		$	25.90
Granted	244,165		30.18		8.40		244,165		30.18
Acquired	—		—		—		132,883		12.93
Exercised	—		—		—		(310,985	)	25.10
Vested	(150,224	)	25.57		7.80		—		—
Forfeited/expired	(46,385	)	27.99		8.50		(48,635	)	28.18
Outstanding at December 31, 2015	479,755		$	28.75	$	8.49	1,054,739		$	25.38
Granted	441,167		32.81		6.15		441,167		32.81
Acquired	—		—		—		1,466,408		15.08
Exercised	—		—		—		(450,296	)	20.02
Vested	(454,360	)	28.74		8.49		—		—
Forfeited/expired	(58,623	)	31.10		7.17		(58,623	)	31.10
Outstanding at December 31, 2016	407,939		$	32.81	$	6.15	2,453,395		$	21.41
Granted	132,414		53.43		9.94		132,414		53.43
Exercised	—		—		—		(1,427,159	)	17.50
Vested	(161,751	)	37.73		7.07		—		—
Forfeited/expired	(47,732	)	37.55		7.03		(47,732	)	37.55
Outstanding at December 31, 2017	330,870		$	37.97	$	7.09	1,110,918		$	29.56
Exercisable/vested at December 31, 2017							780,048		$	25.99

Assumptions of Black-Scholes option pricing model

The fair value of the stock options granted during the years ended December 31, 2017, 2016 and 2015 were estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.

	2017		2016		2015
Expected dividend yield	3.31	%	3.30	%	3.50	%
Risk-free interest rate	2.05	%	1.39	%	1.78	%
Expected stock price volatility	26.7	%	27.9	%	39.1	%
Expected life of options — in years	6.0		6.5		7.0
Weighted average fair value of options granted	$9.94		$6.15		$8.40

Summary of activity for restricted stock units and awards

A summary of the activity for RSUs during the year ended December 31, 2017 is presented below:

	Number of units		Weighted-average grant date fair value per unit
Outstanding at December 31, 2016	298,357		$	32.81
Granted	169,252		51.93
Converted into shares of common stock	(75,639	)	30.73
Forfeited/expired	(11,030	)	47.62
Outstanding at December 31, 2017	380,940		$	41.29

The following table provides information regarding nonvested restricted stock awards:

Nonvested restricted stock awards	Number of awards		Weighted-average acquisition-date fair value
Nonvested at January 1, 2017	365,891		$	46.23
Vested	(277,821	)	46.23
Forfeited	(4,842	)	46.23
Nonvested at December 31, 2017	83,228		$	46.23