Employee Benefit Plans - Stock Compensation Plans (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Stock options outstanding number of shares, balance (in shares)	812,000	946,000	970,000
Stock options outstanding number of shares, granted (in shares)	0	0	116,000
Stock options outstanding number of shares, stock options exercised (in shares)	(111,728)	(122,012)	(127,424)
Stock options outstanding number of shares, forfeited/expired (in shares)	(5,000)	(12,000)	(13,000)
Stock options outstanding number of shares, balance (in shares)	695,000	812,000	946,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Stock options outstanding weighted average exercise price, balance (in dollars per share)	$ 21.98	$ 21.43	$ 20.31
Stock options outstanding weighted average exercise price, granted (in dollars per share)	0.00	0.00	23.51
Stock options outstanding weighted average exercise price, exercised (in dollars per share)	19.22	17.66	15.14
Stock options outstanding weighted average exercise price, forfeited/expired (in dollars per share)	21.73	22.67	17.53
Stock options outstanding weighted average exercise price, balance (in dollars per share)	$ 22.42	$ 21.98	$ 21.43
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Stock options outstanding number of shares, exercisable (in shares)	662,000
Stock options outstanding weighted average exercise price, exercisable (in dollars per share)	$ 22.37
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Stock awards/units outstanding number of shares, balance (in shares)	162,000	278,000	342,000
Stock awards/units outstanding number of shares, granted (in shares)	0	0	272,000
Stock options outstanding number of shares, stock awards/units vested (in shares)	(80,000)	(91,000)	(318,000)
Stock awards/units outstanding number of shares, forfeited/expired (in shares)	(10,000)	(25,000)	(18,000)
Stock awards/units outstanding number of shares, balance (in shares)	72,000	162,000	278,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Stock awards/units outstanding weighted average grant-date fair-value, balance (in dollars per share)	$ 21.45	$ 20.85	$ 20.48
Stock awards/units outstanding weighted average grant-date fair-value, granted (in dollars per share)	0.00	0.00	23.46
Stock awards/units outstanding weighted average grant-date fair-value, vested (in dollars per share)	20.41	19.40	20.96
Stock awards/units outstanding weighted average grant-date fair-value, forfeited/expired (in dollars per share)	20.12	21.91	21.85
Stock awards/units outstanding weighted average grant-date fair-value, balance (in dollars per share)	$ 20.85	$ 20.48	$ 17.83
Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Stock awards/units outstanding number of shares, balance (in shares)	828,000	406,000	158,000
Stock awards/units outstanding number of shares, granted (in shares)	429,000	906,000	286,000
Stock options outstanding number of shares, stock awards/units vested (in shares)	(311,000)	(449,000)	(25,000)
Stock awards/units outstanding number of shares, forfeited/expired (in shares)	(129,000)	(35,000)	(13,000)
Stock awards/units outstanding number of shares, balance (in shares)	817,000	828,000	406,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Stock awards/units outstanding weighted average grant-date fair-value, balance (in dollars per share)	$ 27.65	$ 26.13	$ 22.70
Stock awards/units outstanding weighted average grant-date fair-value, granted (in dollars per share)	29.16	28.86	23.48
Stock awards/units outstanding weighted average grant-date fair-value, vested (in dollars per share)	25.56	27.13	22.77
Stock awards/units outstanding weighted average grant-date fair-value, forfeited/expired (in dollars per share)	27.95	25.76	23.04
Stock awards/units outstanding weighted average grant-date fair-value, balance (in dollars per share)	$ 26.13	$ 22.70	$ 21.33
Restricted Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Stock awards/units outstanding number of shares, balance (in shares)	177,000	181,000	118,000
Stock awards/units outstanding number of shares, granted (in shares)	72,000	57,000	70,000
Stock options outstanding number of shares, stock awards/units vested (in shares)	(55,000)	(57,000)	0
Stock awards/units outstanding number of shares, forfeited/expired (in shares)	(17,000)	(4,000)	(7,000)
Stock awards/units outstanding number of shares, balance (in shares)	177,000	177,000	181,000

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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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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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 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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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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

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

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

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