Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary Information for Restricted Stock Awards and Incentive Compensation Stock Awards

The following table summarizes information for restricted stock awards and incentive compensation stock awards for 2017:

	Restricted Stock - Service Based					Restricted Stock - Performance Based					Incentive Compensation Stock
	Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value
January 1, 2017		307,317		$	125.36		111,317		$	122.22		40,549		$	114.44
Awarded		80,181		$	213.76		47,997		$	207.73		19,981		$	208.68
Distributed		(68,828	)	$	121.40		(17,692	)	$	129.14		(21,784	)	$	108.44
Forfeited		(3,830	)	$	156.40		(1,623	)	$	150.38		(236	)	$	124.41
December 31, 2017		314,840		$	151.84		139,999		$	150.34		38,510		$	166.67

Summary Information for Stock Options

The following table includes summary information for stock options as of December 31, 2017:

	Number of Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Life (years)
Outstanding at January 1, 2017		406,891		$	93.27
Exercised		(104,093	)	$	98.68
Terminated		(840	)	$	80.52
Outstanding at December 31, 2017		301,958		$	91.44		3.6
Exercisable at December 31, 2017		261,380		$	83.37		3.1

Schedule of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the years ended December 31, 2017, 2016 and 2015, unrecognized compensation cost for nonvested awards at December 31, 2017 and the weighted-average period over which unrecognized compensation cost will be recognized:

(add 000, except year data)	Stock Options		Restricted Stock		Incentive Compensation Stock		Directors’ Awards		Total
Stock-based compensation expense recognized for years    ended December 31:
2017	$	684	$	28,657	$	661	$	458	$	30,460
2016	$	1,646	$	17,747	$	442	$	646		20,481
2015	$	2,679	$	9,809	$	376	$	725		13,589
Unrecognized compensation cost at December 31, 2017:	$	292	$	24,116	$	458	$	—	$	24,866
Weighted-average period over which unrecognized    compensation cost will be recognized:	1.1 years		2.0 years		1.6 years			—

Stock-Based Compensation Expense in Future for Outstanding Awards

The following presents expected stock-based compensation expense in future periods for outstanding awards as of December 31, 2017:

(add 000)
2018	$	15,559
2019		8,299
2020		645
2021		269
2022		94
Total	$	24,866