Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

A summary of the Company’s option activity and related information for the three years ended December 31, 2017 is as follows:

	Number of options			Weighted- average price		Weighted- average remaining contractual term (in years)		Aggregate intrinsic value (in millions)
Balance at December 31, 2014		1,343,760		$	27.25
Options granted		456,200			31.69
Options exercised		(270,650	)		19.81
Options cancelled/forfeited/expired		(118,660	)		29.58
Balance at December 31, 2015		1,410,650			29.91
Options granted		881,800			25.26
Options exercised		(368,085	)		27.34
Options cancelled/forfeited/expired		(339,930	)		28.62
Balance at December 31, 2016		1,584,435			28.14
Options granted		299,600			34.66
Options exercised		(398,275	)		28.94
Options cancelled/forfeited/expired		(276,900	)		28.04
Balance at December 31, 2017		1,208,860		$	29.52		4.94	$	21.1
Exercisable at December 31, 2017		325,680		$	28.65		4.04	$	6.0
Expected to vest after December 31, 2017		680,049		$	29.78		5.28	$	11.7

Options Outstanding and Options Exercisable by Exercise Price with Weighted-Average Remaining Contractual Life for Options Outstanding and Weighted-Average Exercise Price

The following table indicates the options outstanding and options exercisable by exercise price with the weighted-average remaining contractual life for the options outstanding and the weighted-average exercise price at December 31, 2017:

	Options Outstanding						Options Exercisable
Exercise price	Number outstanding at December 31, 2017		Weighted- average remaining contractual life (Years)		Weighted- average grant date value		Number exercisable at December 31, 2017		Weighted- average grant date value
$20 – 25		481,510		5.13	$	24.59		125,505	$	24.58
$25 – 30		57,505		3.14	$	28.05		37,300	$	28.91
$30 – 35		654,265		4.94	$	33.07		160,635	$	32.09
$35 – 40		8,780		5.32	$	38.61		2,240	$	38.18
$40 – 45		6,800		6.67	$	40.37		—	$	—
$20 – 45		1,208,860		4.94	$	29.52		325,680	$	28.65

Schedule of Weighted-Average Assumptions Used to Determine Fair Value of Option Granted

The fair value of each option granted was estimated on the date of grant using the Black-Scholes option-pricing model using the following weighted-average assumptions:

	Year Ended December 31,
	2017			2016			2015
Expected term (in years)		5.0			5.0			5.0
Expected volatility		26.1	%		28.7	%		31.1	%
Expected dividend yields		3.0	%		4.1	%		3.2	%
Risk-free interest rates		2.0	%		1.2	%		1.6	%

Summary of Company's Restricted Stock Units Activity

The following table summarizes the activity of the Company’s RSUs, which includes service-based and performance-based awards, for the three years ended December 31, 2017:

				Weighted-		Aggregate
				average		intrinsic
	Number			grant date		value
	of shares			fair value		(in millions)
Balance at December 31, 2014		311,583		$	29.78
RSUs granted		79,300			31.86
RSUs vested		(89,915	)		27.97
RSUs cancelled/forfeited/expired		(80,320	)		31.35
Balance at December 31, 2015		220,648			30.70
RSUs granted		31,900			25.75
RSUs vested		(59,008	)		29.69
RSUs cancelled/forfeited/expired		(68,300	)		29.33
Balance at December 31, 2016		125,240			30.66
RSUs granted		70,960			34.53
RSUs vested		(36,336	)		26.99
RSUs cancelled/forfeited/expired		(66,200	)		32.63
Balance at December 31, 2017		93,664		$	33.62	$	4.4