Common Stock (Details) - USD ($)	3 Months Ended	12 Months Ended			87 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Oct. 23, 2018	Oct. 25, 2017	Oct. 28, 2015	Oct. 23, 2014	Dec. 05, 2013	Sep. 26, 2011
Equity, Class of Treasury Stock [Line Items]
Common stock, outstanding (in shares)	55,983,763	55,983,763	58,798,428		55,983,763
Dividend paid (in dollars per share)	$ 0.08
Stock repurchased (in US dollars)		$ 216,244,000	$ 90,821,000	$ 88,568,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)		3,066,869			15,900,000
Stock repurchased (in US dollars)		$ 216,200,000	$ 10,000	$ 15,000	$ 791,500,000
Remaining authorized repurchase amount (in US dollars)	$ 158,500,000	$ 158,500,000			$ 158,500,000
Common Stock | RepurchaseProgramSept262011
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount (in US dollars)											$ 100,000,000
Common Stock | RepurchaseProgramDec52013
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount (in US dollars)										$ 100,000,000
Common Stock | RepurchaseProgramOct232014
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount (in US dollars)									$ 250,000,000
Common Stock | RepurchaseProgramOct282015
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount (in US dollars)								$ 200,000,000
Common Stock | RepurchaseProgramOct252017
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount (in US dollars)							$ 100,000,000
Common Stock | RepurchaseProgramOct232018
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount (in US dollars)						$ 200,000,000