Stock-Based Compensation - Additional Information (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]
Shares authorized for grant under the plan	39,800,000.0
Percentage of voting interest to be held by optionee	10.00%
Exercise price as a percentage of fair value at the time of grant	110.00%
Vesting period	4 years
Maximum months after sale event where awards fully vest when service relationship terminated without cause	18 months
Minimum number of days that may be granted to terminated employee to exercise awards prior to termination	15 days
Share-based compensation arrangement by share-based payment award, options, vested in period, fair value	$ 2,900	$ 7,400	$ 12,300
Total unrecognized estimated unvested stock option compensation cost	$ 5,000
Weighted-average period of recognition of unrecognized compensation cost (years)	1 year 9 months
Total intrinsic value of options exercised during the period	$ 58,500	49,800	47,100
Unvested options	200,000
Aggregate intrinsic value of unvested options	$ 13,400
Weighted-average exercise price of unvested options	$ 91.71
Weighted-average remaining contractual term of unvested stock options (years)	8 years 3 months
Employee service share-based compensation, cash received from exercise of stock options	$ 47,600
Tax benefit from exercise of stock options	20,500
Stock-based compensation expense	53,154	33,347	33,951
Fair value of stock options and restricted stock awards assumed in connection with acquisitions	$ 0	$ 0	$ 3,528
Performance Shares [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of awards granted	26,227	35,000	34,450
Value of the restricted stock units on the grant date	$ 120.94	$ 78.71	$ 81.61
Stock-based compensation expense	$ 1,800	$ 2,200	$ 3,100
Restricted stock units earned	33,187
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of awards granted	85,132	63,462	51,795
Value of the restricted stock units on the grant date	$ 106.95	$ 84.61	$ 86.38
Stock-based compensation expense	$ 6,600	$ 400	$ 400
Share-based compensation arrangement by share-based payment award, shares issued in period	104,910	35,000	115,485
Restricted stock units earned	11,059
Restricted Stock Units (RSUs) [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of awards granted	762,732	488,622	344,500
Value of the restricted stock units on the grant date	$ 109.56	$ 88.51	$ 86.34
Stock-based compensation expense	$ 37,300	$ 19,100	$ 12,500
Restricted stock units earned	261,618	162,019	85,713
Share-based compensation arrangement by share-based payment award, equity instruments other than options, nonvested, number	1,262,496	838,327	571,462
Deferred Stock Units [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period	1 year
Number of awards granted	18,018	38,400
Stock-based compensation expense	$ 2,600	$ 1,900	$ 4,000
Restricted stock units earned	159,599
Diversified deferred stock awards	29,500
Series of Individually Immaterial Business Acquisitions [Member] \| Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Value of the restricted stock units on the grant date			$ 90.48
Stock-based compensation expense	$ 600	$ 1,200	$ 600
Share-based compensation arrangement by share-based payment award, shares issued in period			68,451
Stock issued during period, value, restricted stock award			$ 6,200
Minimum [Member] \| Performance Shares [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period	1 year
Minimum [Member] \| Restricted Stock Units (RSUs) [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period	3 years
Maximum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period of options from the date of grant	10 years
Expiration period for optionee who meets the 10% criteria	5 years
Maximum [Member] \| Performance Shares [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period	3 years
Maximum [Member] \| Restricted Stock Units (RSUs) [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period	4 years

Exercise Price Minimum Percent of Fair Market Value Threshold for Issuance of I S O to 10% shareholder

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Maximum Term After Sale Event Where Awards Fully Vest When Service Relationship Terminated Without Cause

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Maximum Term That May Be Granted To Terminated Employee To Exercise Awards Prior To Termination

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Share based compensation arrangement by share based payment award, award expiration dating conditional.

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Threshold of total combined voting interest of all class of stock for ISO.

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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 equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

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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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Balance held at close of period in number of shares.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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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 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 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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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share instruments newly issued under a share-based compensation plan.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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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Value of stock related to Restricted Stock Awards issued during the period, net of the stock value of such awards forfeited.

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