Stock Award Plans (Details) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Award Plans [Abstract]
Compensation cost	$ 11,675,000	$ 11,104,000	$ 11,591,000
Income tax benefit	4,378,000	4,120,000	4,358,000
Share-based Compensation Plans Combined Disclosure [Abstract]
Intrinsic value of stock options exercised	266,000	2,555,000	11,671,000
Tax benefit from stock options exercised	100,000	948,000	4,388,000
Intrinsic value of restricted stock vesting	6,928,000	10,270,000	14,847,000
Tax benefit from restricted stock vesting	2,598,000	3,810,000	5,583,000
Fair value of options vested	2,495,000	2,180,000	3,759,000
Fair value of restricted stock vested	$ 6,928,000	$ 10,270,000	$ 14,847,000
Fair value of stock options granted (in dollars per share)	$ 17.30	$ 25.18	$ 36.05
Fair value of stock options granted	$ 3,231,000	$ 2,893,000	$ 4,226,000
Stock Options [Member]
Share-based Compensation Plans Combined Disclosure [Abstract]
Unrecognized compensation cost related to unvested awards	$ 3,422,000
Weighted average period of recognition in years	1 year 4 months 24 days
Fair Value Assumptions [Abstract]
Dividend yield	0.00%	0.00%	0.00%
Average risk-free interest rate	1.50%	1.30%	2.00%
Stock price volatility	30.00%	33.00%	33.00%
Estimated option term	6 years	6 years
Stock Options [Member] \| Minimum [Member]
Fair Value Assumptions [Abstract]
Estimated option term			6 years
Stock Options [Member] \| Maximum [Member]
Fair Value Assumptions [Abstract]
Estimated option term			7 years
Restricted Stock [Member]
Share-based Compensation Plans Combined Disclosure [Abstract]
Unrecognized compensation cost related to unvested awards	$ 18,055,000
Weighted average period of recognition in years	3 years 1 month 6 days
Employee Stock Award Plan [Member]
Stock Award Plan Information [Abstract]
Term of grant	7 years
Vesting period	3 years
Shares available for future grants (in shares)	1,987,512
Options Exercisable [Abstract]
Stock options exercisable (in shares)	321,942	239,518	157,140
Employee Stock Award Plan [Member] \| Stock Options [Member]
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period Start, (in shares)	430,432	322,956	379,604
Granted (in shares)	186,706	114,894	75,204
Exercised (in shares)	0	0	(119,276)
Canceled or expired (in shares)	(16,017)	(7,418)	(12,576)
Outstanding at Period End (in shares)	601,121	430,432	322,956
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start (in dollars per share)	$ 71.01	$ 69.95	$ 55.42
Granted (in dollars per share)	53.50	74.99	98.91
Exercised (in dollars per share)	0	0	42.07
Canceled or expired (in dollars per share)	80.17	86.28	68.89
Outstanding at Period End (in dollars per share)	65.33	$ 71.01	$ 69.95
Employee Stock Award Plan [Member] \| Stock Options [Member] \| First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	36.35
Range of Exercise Prices, lower limit (in dollars per share)	$ 31.35
Options Outstanding [Abstract]
Number Outstanding (in shares)	16,910
Weighted Average Remaining Contractual Life	1 month 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 32.82
Options Exercisable [Abstract]
Number Exercisable (in shares)	16,910
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 32.82
Employee Stock Award Plan [Member] \| Stock Options [Member] \| Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	51.23
Range of Exercise Prices, lower limit (in dollars per share)	$ 46.74
Options Outstanding [Abstract]
Number Outstanding (in shares)	212,335
Weighted Average Remaining Contractual Life	4 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 50.03
Options Exercisable [Abstract]
Number Exercisable (in shares)	56,629
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 46.74
Employee Stock Award Plan [Member] \| Stock Options [Member] \| Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	74.99
Range of Exercise Prices, lower limit (in dollars per share)	$ 64.89
Options Outstanding [Abstract]
Number Outstanding (in shares)	302,735
Weighted Average Remaining Contractual Life	4 years 1 month 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 70.29
Options Exercisable [Abstract]
Number Exercisable (in shares)	202,309
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 69.51
Employee Stock Award Plan [Member] \| Stock Options [Member] \| Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	96.85
Range of Exercise Prices, lower limit (in dollars per share)	$ 93.64
Options Outstanding [Abstract]
Number Outstanding (in shares)	33,987
Weighted Average Remaining Contractual Life	4 years 1 month 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 94.31
Options Exercisable [Abstract]
Number Exercisable (in shares)	22,658
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 94.31
Employee Stock Award Plan [Member] \| Stock Options [Member] \| Fifth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	104.37
Range of Exercise Prices, lower limit (in dollars per share)	$ 101.46
Options Outstanding [Abstract]
Number Outstanding (in shares)	35,154
Weighted Average Remaining Contractual Life	4 years 2 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 102.60
Options Exercisable [Abstract]
Number Exercisable (in shares)	23,436
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 102.60
Employee Stock Award Plan [Member] \| Stock Options [Member] \| Full Exercise Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	104.37
Range of Exercise Prices, lower limit (in dollars per share)	$ 31.35
Options Outstanding [Abstract]
Number Outstanding (in shares)	601,121
Weighted Average Remaining Contractual Life	4 years 2 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 65.33
Aggregate Intrinsic Value, Options Outstanding	$ 4,175,000
Options Exercisable [Abstract]
Number Exercisable (in shares)	321,942
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 67.73
Aggregate Intrinsic Value, Options Exercisable	$ 1,747,000
Employee Stock Award Plan [Member] \| Restricted Stock [Member]
Unvested Restricted Stock Award Shares [Roll Forward]
Nonvested balance beginning of period (in shares)	311,727	321,453	399,278
Granted (in shares)	190,610	122,740	97,706
Vested (in shares)	(105,109)	(113,958)	(141,870)
Forfeited (in shares)	(19,573)	(18,508)	(33,661)
Nonvested balance end of period (in shares)	377,655	311,727	321,453
Weighted Average Grant Date Fair Value Per Share [Abstract]
Nonvested balance beginning of period (in dollars per share)	$ 75.73	$ 71.04	$ 54.92
Granted (in dollars per share)	53.56	75.04	97.46
Vested (in dollars per share)	69.93	60.73	45.64
Forfeited (in dollars per share)	76.06	82.00	63.56
Nonvested balance end of period (in dollars per share)	$ 66.14	$ 75.73	$ 71.04
2000 Director Plan [Member]
Stock Award Plan Information [Abstract]
Term of grant	10 years
Vesting period	6 months
Shares available for future grants (in shares)	522,457
Options Exercisable [Abstract]
Stock options exercisable (in shares)	205,429	220,429	298,334
2000 Director Plan [Member] \| Stock Options [Member]
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period Start, (in shares)	220,429	298,334	320,322
Granted (in shares)			42,000
Exercised (in shares)	(9,000)	(77,905)	(63,988)
Canceled or expired (in shares)	(6,000)
Outstanding at Period End (in shares)	205,429	220,429	298,334
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start (in dollars per share)	$ 64.37	$ 60.01	$ 50.64
Granted (in dollars per share)			99.52
Exercised (in dollars per share)	35.72	47.65	39.08
Canceled or expired (in dollars per share)	99.52
Outstanding at Period End (in dollars per share)	64.60	$ 64.37	$ 60.01
2000 Director Plan [Member] \| Stock Options [Member] \| First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	36.82
Range of Exercise Prices, lower limit (in dollars per share)	$ 29.60
Options Outstanding [Abstract]
Number Outstanding (in shares)	21,000
Weighted Average Remaining Contractual Life	10 months 24 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 32.69
Options Exercisable [Abstract]
Number Exercisable (in shares)	21,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 32.69
2000 Director Plan [Member] \| Stock Options [Member] \| Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	56.45
Range of Exercise Prices, lower limit (in dollars per share)	$ 41.24
Options Outstanding [Abstract]
Number Outstanding (in shares)	71,276
Weighted Average Remaining Contractual Life	2 years 8 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 52.34
Options Exercisable [Abstract]
Number Exercisable (in shares)	71,276
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 52.34
2000 Director Plan [Member] \| Stock Options [Member] \| Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	62.48
Range of Exercise Prices, lower limit (in dollars per share)	$ 61.89
Options Outstanding [Abstract]
Number Outstanding (in shares)	41,153
Weighted Average Remaining Contractual Life	4 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 62.34
Options Exercisable [Abstract]
Number Exercisable (in shares)	41,153
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 62.34
2000 Director Plan [Member] \| Stock Options [Member] \| Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	99.52
Range of Exercise Prices, lower limit (in dollars per share)	$ 75.17
Options Outstanding [Abstract]
Number Outstanding (in shares)	72,000
Weighted Average Remaining Contractual Life	5 years 8 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 87.35
Options Exercisable [Abstract]
Number Exercisable (in shares)	72,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 87.35
2000 Director Plan [Member] \| Stock Options [Member] \| Sixth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	99.52
Range of Exercise Prices, lower limit (in dollars per share)	$ 29.60
2000 Director Plan [Member] \| Stock Options [Member] \| Full Exercise Price Range [Member]
Options Outstanding [Abstract]
Number Outstanding (in shares)	205,429
Weighted Average Remaining Contractual Life	4 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 64.60
Aggregate Intrinsic Value, Options Outstanding	$ 1,891,000
Options Exercisable [Abstract]
Number Exercisable (in shares)	205,429
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 64.60
Aggregate Intrinsic Value, Options Exercisable	$ 1,891,000
2000 Director Plan [Member] \| Restricted Stock [Member]
Unvested Restricted Stock Award Shares [Roll Forward]
Nonvested balance beginning of period (in shares)	1,791	292	384
Granted (in shares)	23,074	20,350	8,160
Vested (in shares)	(24,518)	(18,851)	(8,252)
Nonvested balance end of period (in shares)	347	1,791	292
Weighted Average Grant Date Fair Value Per Share [Abstract]
Nonvested balance beginning of period (in dollars per share)	$ 68.73	$ 99.52	$ 75.65
Granted (in dollars per share)	64.89	78.52	99.52
Vested (in dollars per share)	65.17	79.77	98.41
Nonvested balance end of period (in dollars per share)	$ 64.89	$ 68.73	$ 99.52

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Tax benefit from restricted stock vesting during the reporting period.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Net number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Intrinsic value of equity-based compensation awards vested. Excludes stock and unit options.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

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Number of share options (or share units) exercised during the current period.

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