Stockholders' Equity and Stock Incentive Plans (Restricted Stock Units, Performance Stock Units and Career Shares) (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]
Share-based compensation expense	$ 17,413	$ 15,518	$ 19,264
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	442,879	542,220	541,016
Share-based compensation expense	$ 7,463	$ 8,883	$ 9,909
Non-Option Award Activity [Roll Forward]
Outstanding, beginning of period	1,961,118	2,320,826	2,534,496
Canceled	(38,964)	(30,400)	(40,800)
Vested / awarded	(727,821)	(871,528)	(713,886)
Outstanding, end of period	1,637,212	1,961,118	2,320,826
Granted, weighted average grant date fair value (in USD per share)	$ 27.40	$ 18.06	$ 19.05
Total unrecognized share-based compensation costs related to unvested stock options	$ 0
Total unrecognized share-based compensation costs related to unvested stock options, period for recognition	2 years 6 months 2 days
Performance Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	275,305	241,235	240,160
Share-based compensation expense	$ 7,381	$ 3,353	$ 5,135
Non-Option Award Activity [Roll Forward]
Outstanding, beginning of period	1,129,078	1,249,480	1,411,640
Canceled	0	0	(2,677)
Vested / awarded	(268,429)	(213,365)	(663,945)
Outstanding, end of period	1,062,547	1,129,078	1,249,480
Granted, weighted average grant date fair value (in USD per share)	$ 28.94	$ 17.75	$ 16.75
Total unrecognized share-based compensation costs related to unvested stock options	$ 6,900
Total unrecognized share-based compensation costs related to unvested stock options, period for recognition	2 years 8 months 13 days
Shares to be issued to settle PSUs	1,400,000
Evaluation of performance conditions, period	3 years
Awards if no conditions met, percentage	0.00%
Awards if only threshhold performance met, percentage	50.00%
Awards for target performance, percentage	100.00%
Awards for maximum performance, percentage (up to 200%)	200.00%
Award vesting period	3 years
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 1,193	$ 1,974	$ 2,821
Non-Option Award Activity [Roll Forward]
Total unrecognized share-based compensation costs related to unvested stock options	$ 200
Total unrecognized share-based compensation costs related to unvested stock options, period for recognition	1 year 4 months 26 days
Performance Shares Adjustment [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	(73,407)	(148,272)	264,306
Career Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	66,000	73,064	103,018
Share-based compensation expense	$ 1,376	$ 1,308	$ 1,399
Non-Option Award Activity [Roll Forward]
Outstanding, beginning of period	1,041,639	968,575	896,585
Canceled	(11,236)	0	0
Vested / awarded	(82,944)	0	(31,028)
Outstanding, end of period	1,013,459	1,041,639	968,575
Granted, weighted average grant date fair value (in USD per share)	$ 20.41	$ 19.01	$ 12.51
Total unrecognized share-based compensation costs related to unvested stock options	$ 1,100
Executive Officer \| Career Shares
Non-Option Award Activity [Roll Forward]
Award eligibility, minimum age	55 years
Award requisite service period	10 years
Service period, Tranche 1	10 years
Service period, Tranche 2	15 years
Service period, Tranche 3	20 years
Stock Incentive Plan 2012 [Member] \| Stock Options
Non-Option Award Activity [Roll Forward]
Award vesting period	3 years
Common Stock
Non-Option Award Activity [Roll Forward]
Stock Issued During Period, Shares, Performance Stock Award, Net	173,653	159,027	481,749
Common Stock \| PSU - Nov 2013 [Domain]
Non-Option Award Activity [Roll Forward]
Shares to be issued to settle PSUs	0.80
Stock Issued During Period, Shares, Performance Stock Award, Gross	268,429
Stock Issued During Period, Shares, Performance Stock Award, Taxes	94,776
Stock Issued During Period, Shares, Performance Stock Award, Net	173,653
Common Stock \| PSU - Dec 2012 [Domain]
Non-Option Award Activity [Roll Forward]
Shares to be issued to settle PSUs	0.59
Stock Issued During Period, Shares, Performance Stock Award, Gross	213,365
Stock Issued During Period, Shares, Performance Stock Award, Taxes	54,338
Stock Issued During Period, Shares, Performance Stock Award, Net	159,027

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Share-based Compensation Arrangement by Share-based Payment Award, Awards for Maximum Performance, Percentage

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Stock Issued During Period, Shares, Performance Stock Award, Taxes

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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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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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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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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 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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