Stock-Based Compensation - Performance-Based Restricted Stock Units (Narrative) (Details) $ in Millions									1 Months Ended		3 Months Ended		12 Months Ended
	Aug. 03, 2016 shares	Jun. 27, 2016 shares	Jun. 20, 2016 shares	May 05, 2016 shares	Mar. 31, 2016 employee shares	Dec. 14, 2015 shares	Sep. 28, 2015 shares	Mar. 30, 2015 executive_officer shares	May 31, 2017 employee shares	Mar. 31, 2017 employee shares	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PBU expense reversed | $													$ 7.1	$ 5.1	$ 3.9
PBUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (shares)													333,800,000	1,350,750,000	2,493,333,000
2008 EIP | PBUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (shares)		641,750
Vested PBUs to be paid in whole shares of common stock (as a percent)		40.00%								100.00%
PBUs that vest and become payable based on the cumulative revenue from continuing operations (as a percent)										65.00%
PBUs that vest and become payable on the cumulative adjusted EBITDA from continuing operations (as a percent)										35.00%
Performance period		2 years								2 years
PBUs that will become vested and payable at the threshold performance level (as a percent)		35.00%								35.00%
PBUs that will become vested and payable at the target performance level (as a percent)		100.00%								100.00%
PBUs that will become vested and payable at the maximum performance level (as a percent)		150.00%
Maximum PBUs that may become vested and payable (as a percent)										100.00%
PBUs that shall become vested and payable if performance does not equal or exceed the applicable threshold performance level (as a percent)		0.00%								0.00%
Fair market value of shares equal to the number of PBUs being settled (as a percent)		60.00%
PBU expense reversed | $											$ (0.6)	$ (0.8)			$ (1.4)
Executive officers | 2008 EIP | PBUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees granted share-based compensation awards					5			8	1	6
Awards granted (shares)								1,325,000
PBUs that will become vested and payable at the threshold performance level (as a percent)				35.00%
PBUs that will become vested and payable at the target performance level (as a percent)				100.00%
PBUs that will become vested and payable at the maximum performance level (as a percent)				150.00%
PBUs that shall become vested and payable if performance does not equal or exceed the applicable threshold performance level (as a percent)				0.00%
Senior leaders | 2008 EIP | PBUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees granted share-based compensation awards | employee					3				1	6
Awards granted (shares)	10,000		30,000	60,000	609,000	45,000	1,123,333
Share Based Compensation Arrangement by Share Based Payment Award Performance Units Settlement in Common Stock Percentage				43.00%	43.00%
Vested PBUs to be paid in whole shares of common stock (as a percent)			40.00%
Performance period			2 years	2 years	2 years
PBUs that will become vested and payable at the threshold performance level (as a percent)			35.00%
PBUs that will become vested and payable at the target performance level (as a percent)			100.00%
PBUs that will become vested and payable at the maximum performance level (as a percent)			150.00%
PBUs that shall become vested and payable if performance does not equal or exceed the applicable threshold performance level (as a percent)			0.00%
Fair market value of shares equal to the number of PBUs being settled (as a percent)			60.00%	57.00%	57.00%
Executive officers and senior leaders | 2008 EIP | PBUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (shares)									59,000	274,800
Vested PBUs to be paid in whole shares of common stock (as a percent)									100.00%
PBUs that vest and become payable based on the cumulative revenue from continuing operations (as a percent)									65.00%
PBUs that vest and become payable on the cumulative adjusted EBITDA from continuing operations (as a percent)									35.00%
Performance period									2 years
PBUs that will become vested and payable at the threshold performance level (as a percent)					35.00%				35.00%
PBUs that will become vested and payable at the target performance level (as a percent)					100.00%				100.00%
PBUs that will become vested and payable at the maximum performance level (as a percent)					150.00%
Maximum PBUs that may become vested and payable (as a percent)									100.00%
PBUs that shall become vested and payable if performance does not equal or exceed the applicable threshold performance level (as a percent)					0.00%				0.00%