Subsequent Events - KWE Merger (Details) - Subsequent Event [Member] £ / shares in Units, $ / shares in Units, £ in Millions, $ in Millions	Oct. 23, 2017 USD ($) $ / shares shares	Oct. 23, 2017 GBP (£) £ / shares shares	Oct. 20, 2017 $ / shares	Oct. 20, 2017 £ / shares	Oct. 19, 2017
Subsequent Event [Line Items]
Common stock, par value (in dollars per share) | $ / shares	$ 0.0001		$ 0.0001
KWE [Member] | United Kingdom, Pounds [Member]
Subsequent Event [Line Items]
Foreign currency exchange rate					1.3182
Original Merger Offer [Member] | KWE [Member]
Subsequent Event [Line Items]
Dividends payable (per share) | (per share)			0.16	£ 0.12
New Merger Offer [Member] | KWE [Member]
Subsequent Event [Line Items]
Dividends payable (per share) | (per share)			$ 0.17	£ 0.13
KWE [Member]
Subsequent Event [Line Items]
Equity interest issued (in shares)	37,226,695	37,226,695
Cash consideration to shareholders	$ 697.2	£ 528.6
Cash consideration to shareholders paid by parent	380.3	288.3
Cash consideration to shareholders paid by KWE	$ 316.9	£ 240.3
Settlement period	14 days	14 days
KWE [Member] | Original Merger Offer [Member]
Subsequent Event [Line Items]
Share consideration to shareholders (in shares)	0.667	0.667
KWE [Member] | New Merger Offer [Member]
Subsequent Event [Line Items]
Share consideration to shareholders (in shares)	0.3854	0.3854
Purchase of interest by parent (in pence per share) | £ / shares		£ 3.00
Purchase of interest by KWE (in pence per share) | £ / shares		£ 2.50
Eligible ordinary shares (in shares)	11,227,921	11,227,921
Percent of eligible ordinary shares	11.65%	11.65%
Unsatisfied share elections (in shares)	9,974,888	9,974,888
KWE [Member] | Merger Offer, Mix and Match Facility [Member]
Subsequent Event [Line Items]
Share consideration to shareholders (in shares)	0.5923	0.5923
Purchase of interest by KWE (in pence per share) | £ / shares		£ 8.59
Eligible ordinary shares (in shares)	30,889,536	30,889,536
Percent of eligible ordinary shares	32.05%	32.05%