Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Ordinary Shares	Additional Paid-In Capital	Treasury Shares	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total
Balance at beginning of period at Dec. 31, 2018	$ 0.5	$ 575.4	$ (418.1)	$ (142.3)	$ 753.2	$ 768.7
Balance at beginning of period, shares at Dec. 31, 2018	41.6		7.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)					35.8	35.8
Other comprehensive income (loss)				(1.2)		(1.2)
Stock-based compensation		(6.6)	$ 7.0			0.4
Stock-based compensation, shares	0.1		(0.1)
Purchase of treasury shares			$ (34.0)			(34.0)
Purchase of treasury shares, shares	(0.7)		0.7
Dividends on ordinary shares					(16.6)	(16.6)
Balance at end of period at Mar. 31, 2019	$ 0.5	568.8	$ (445.1)	(143.5)	772.4	753.1
Balance at end of period, shares at Mar. 31, 2019	41.0		7.8
Balance at beginning of period at Dec. 31, 2018	$ 0.5	575.4	$ (418.1)	(142.3)	753.2	768.7
Balance at beginning of period, shares at Dec. 31, 2018	41.6		7.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)						63.8
Other comprehensive income (loss)						(3.3)
Balance at end of period at Jun. 30, 2019	$ 0.5	571.2	$ (465.1)	(145.6)	784.1	745.1
Balance at end of period, shares at Jun. 30, 2019	40.6		8.2
Balance at beginning of period at Mar. 31, 2019	$ 0.5	568.8	$ (445.1)	(143.5)	772.4	753.1
Balance at beginning of period, shares at Mar. 31, 2019	41.0		7.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)					28.0	28.0
Other comprehensive income (loss)				(2.1)		(2.1)
Stock-based compensation		2.4	$ 1.7			4.1
Stock-based compensation, shares	0.1		(0.1)
Purchase of treasury shares			$ (21.7)			(21.7)
Purchase of treasury shares, shares	(0.5)		0.5
Dividends on ordinary shares					(16.3)	(16.3)
Balance at end of period at Jun. 30, 2019	$ 0.5	571.2	$ (465.1)	(145.6)	784.1	745.1
Balance at end of period, shares at Jun. 30, 2019	40.6		8.2
Balance at beginning of period at Dec. 31, 2019	$ 0.5	574.7	$ (524.9)	(162.4)	781.0	$ 668.9
Balance at beginning of period, shares at Dec. 31, 2019	39.0		9.8			39.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)					(36.3)	$ (36.3)
Other comprehensive income (loss)				8.2		8.2
Stock-based compensation		1.0	$ 1.7			2.7
Purchase of treasury shares			$ (25.0)			(25.0)
Purchase of treasury shares, shares	(0.8)		0.8
Dividends on ordinary shares					(15.5)	(15.5)
Balance at end of period at Mar. 31, 2020	$ 0.5	575.7	$ (548.2)	(154.2)	729.2	603.0
Balance at end of period, shares at Mar. 31, 2020	38.2		10.6
Balance at beginning of period at Dec. 31, 2019	$ 0.5	574.7	$ (524.9)	(162.4)	781.0	$ 668.9
Balance at beginning of period, shares at Dec. 31, 2019	39.0		9.8			39.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)						$ (164.7)
Other comprehensive income (loss)						6.3
Balance at end of period at Jun. 30, 2020	$ 0.5	576.3	$ (547.3)	(156.1)	585.4	$ 458.8
Balance at end of period, shares at Jun. 30, 2020	38.3		10.5			38.3
Balance at beginning of period at Mar. 31, 2020	$ 0.5	575.7	$ (548.2)	(154.2)	729.2	$ 603.0
Balance at beginning of period, shares at Mar. 31, 2020	38.2		10.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)					(128.4)	(128.4)
Other comprehensive income (loss)				(1.9)		(1.9)
Stock-based compensation		0.6	$ 0.9			1.5
Stock-based compensation, shares	0.1		(0.1)
Dividends on ordinary shares					(15.4)	(15.4)
Balance at end of period at Jun. 30, 2020	$ 0.5	$ 576.3	$ (547.3)	$ (156.1)	$ 585.4	$ 458.8
Balance at end of period, shares at Jun. 30, 2020	38.3		10.5			38.3