Stock-Based Compensation, Stock Award and Incentive Plan and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock available for issuance (in shares)			880,000
Term of stock options granted under Plan	10 years
Vesting period, generally, for stock options granted under the plan	3 years
Share based compensation costs	$ 4,100	$ 3,500	$ 4,000
Tax benefit of share-based compensation	$ 1,100	$ 1,400	$ 1,600
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture rate assumed	8.71%	7.38%	7.34%
Weighted average grant date fair value for stock options granted (in dollars per share)	$ 30.28	$ 14.34	$ 22.68
Weighted average grant date fair value for stock options vested (in dollars per share)	$ 18.45	$ 20.94	$ 17.83
Total intrinsic value of stock options exercised	$ 11,700	$ 4,900	$ 2,400
Weighted Average Assumptions [Abstract]
Expected life	6 years 4 months 24 days	6 years 5 months 23 days	6 years 4 months 24 days
Interest rate	2.04%	1.72%	1.52%
Volatility	36.61%	36.75%	36.86%
Expected dividend yield	0.26%	0.54%	0.33%
Stock Options [Roll Forward]
Balance, beginning of year (in shares)	1,198,725
Granted (in shares)	187,533
Exercised (in shares)	(353,636)
Canceled (in shares)	(35,783)
Balance, end of year (in shares)	996,839	1,198,725
Exercisable, end of year (in shares)	596,446
Weighted Average Exercise Price Per Share [Abstract]
Balance, beginning of year (in dollars per share)	$ 41.66
Granted (in dollars per share)	77.99
Exercised (in dollars per share)	41.56
Canceled (in dollars per share)	50.47
Balance, end of year (in dollars per share)	48.21	$ 41.66
Exercisable, end of year (in dollars per share)	$ 41.01
Weighted Average Remaining Contractual Life [Abstract]
Outstanding options, end of year	6 years 3 months 25 days
Exercisable options, end of year	4 years 11 months 8 days
Aggregate Intrinsic Value [Abstract]
Outstanding options, end of year	$ 22,200
Exercisable options, end of year	$ 16,600
Additional Information [Abstract]
Closing stock price on last business day of the period (in dollars per share)	$ 68.85
Weighted average intrinsic value of options exercised (in dollars per share)	$ 32.95	$ 32.34	$ 32.07
Unrecognized stock-based compensation expense	$ 4,500
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	3 years
Nonvested Stock Options [Member]
Stock Options [Roll Forward]
Balance, beginning of year (in shares)	431,412
Granted (in shares)	187,533
Vested (in shares)	(183,679)
Canceled (in shares)	(34,873)
Balance, end of year (in shares)	400,393	431,412
Weighted Average Exercise Price Per Share [Abstract]
Balance, beginning of year (in dollars per share)	$ 45.61
Granted (in dollars per share)	77.99
Vested (in dollars per share)	48.78
Canceled (in dollars per share)	50.08
Balance, end of year (in dollars per share)	$ 58.94	$ 45.61
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation costs	$ 5,900	$ 5,800	$ 8,800
Additional Information [Abstract]
Unrecognized stock-based compensation expense	$ 5,100
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	3 years