Summary of Significant Accounting Policies - Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Employee stock-based awards
Weighted Average Common Shares Outstanding-Basic (in shares)	286,528,000	285,259,000
Stock-based compensation	$ 8,519	$ 7,384
Stock-based compensation expense (income), net of tax	$ 7,935	$ 6,833
Stock-based compensation expense per basic and diluted share (in dollars per share)	$ 0.03	$ 0.02
Share-Based Compensation, aggregate disclosures
Employee stock-based awards, unrecognized compensation costs on nonvested awards	$ 72,353
Employee stock-based awards, unrecognized compensation costs on nonvested awards, weighted average period of recognition	2 years 2 months 1 day
Stock Options
Summary of option activity
Options outstanding balance, beginning of period (in shares)	4,271,834
Options granted (in shares)	920,706
Options exercised (in shares)	(99,334)
Options forfeited (in shares)	(6,007)
Options expired (in shares)	(9,629)
Options outstanding balance, end of period (in shares)	5,077,570
Options exercisable balance (in shares)	3,258,982
Options expected to vest (in shares)	1,691,146
Performance units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options
Non-vested at the beginning of the period (in shares)	667,101
Granted (in shares)	380,856
Vested (in shares)	(169,523)
Forfeited (in shares)	(19,666)
Non-vested at the end of the period (in shares)	858,768
Total fair value of shares or units vested	$ 6,503	$ 3,033
Performance units \| Two Thousand Seventeen [Member]
Performance units disclosure
Percentage of achievement of the predefined revenue and ROIC targets	100.00%
Performance units \| Two Thousand Eighteen [Member]
Performance units disclosure
Percentage of achievement of the predefined revenue and ROIC targets	100.00%
Performance units \| Two Thousand Nineteen [Member]
Performance units disclosure
Percentage of achievement of the predefined revenue and ROIC targets	100.00%
Original PU Awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options
Non-vested at the beginning of the period (in shares)	967,049
Granted (in shares)	380,856
Vested (in shares)	(169,523)
Forfeited (in shares)	(4,816)
Non-vested at the end of the period (in shares)	1,173,566
PUs Adjustment
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options
Non-vested at the beginning of the period (in shares)	(299,948)
Granted (in shares)	0
Vested (in shares)	0
Forfeited (in shares)	(14,850)
Non-vested at the end of the period (in shares)	(314,798)
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options
Non-vested at the beginning of the period (in shares)	1,196,566
Granted (in shares)	621,281
Vested (in shares)	(453,167)
Forfeited (in shares)	(18,075)
Non-vested at the end of the period (in shares)	1,346,605
Total fair value of shares or units vested	$ 15,333	$ 15,330

Impact of stock-based compensation expense on basic and diluted earnings per share.

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

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

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