Shareholders' Equity - Prospectus Supplement (Details) |
Mar. 13, 2017
USD ($)
shares
|
Mar. 08, 2017
shares
|
Mar. 07, 2017
£ / shares
shares
|
Jun. 30, 2017
$ / shares
|
Dec. 31, 2016
$ / shares
|
Nov. 10, 2014
USD ($)
|
---|---|---|---|---|---|---|
Class of Stock [Line Items] | ||||||
New issues (shares) | shares | 10,350,000 | 9,000,000 | ||||
Common stock, par value (in dollars per share) | (per share) | £ 0.01 | $ 0.01 | $ 0.01 | |||
Sale of stock, price per share (in dollars per share) | £ / shares | 27.8 | |||||
Proceeds from issuance of common stock | $ 288,100,000 | |||||
Maximum common stock value authorized under prospectus supplement | $ 150,000,000 | |||||
Over-Allotment Option | ||||||
Class of Stock [Line Items] | ||||||
Proceeds from issuance of common stock | $ 37,600,000 | |||||
Underwriters | ||||||
Class of Stock [Line Items] | ||||||
Sale of stock, price per share (in dollars per share) | £ / shares | £ 26.7 | |||||
Underwriters | Over-Allotment Option | ||||||
Class of Stock [Line Items] | ||||||
New issues (shares) | shares | 1,350,000 | |||||
Additional purchase of shares, exercise term | 30 days |