Stock compensation plans (Tables)

12 Months Ended

Dec. 31, 2014

Weighted-Average Assumptions used to Estimate Fair Value of Options Granted

The fair value of options granted in 2014, 2013 and 2012 was estimated at the date of grant using a multiple point Black-Scholes option pricing model. The following weighted-average assumptions were used:



	2014		2013		2012
Risk-free interest rate	1.45	%	0.75	%	0.81	%
Expected life of option	4.89 years		4.87 years		4.85 years
Expected dividend yield	1.34	%	1.73	%	2.28	%
Expected volatility	21.44	%	24.65	%	28.46	%

Weighted-Average Assumptions used to Estimate Fair Value of Non-Vested Shares Granted

The following weighted-average assumptions were used:



	2014		2013		2012
Risk-free interest rate	0.65	%	0.36	%	0.37	%
Expected dividend yield	1.34	%	1.71	%	2.24	%

Summary of Stock Option Activity

The following table summarizes the option activity during 2014:



	Shares Subject to Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life In Years	Aggregate Intrinsic Value
						(Dollars in thousands)
Outstanding, beginning of the year	1,279,480		$	65.05
Granted	343,580		101.45
Exercised	(362,719	)	60.86
Forfeited or expired	(26,669	)	87.37
Outstanding, end of the year	1,233,672		75.93		7.3	$	47,974
Exercisable, end of the year	647,425		$	64.82	6.1	$	32,373

Summary of Non-Vested Restricted Stock Unit Activity

The Company recorded $4.6 million of expense related to the portion of the shares underlying options