Income Taxes - Narrative (Details)		3 Months Ended								12 Months Ended
	Oct. 31, 2016 $ / shares	Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares
Operating Loss Carryforwards [Line Items]
Stock distribution ratio	5
Common stock dividend paid in lieu of fractional shares (usd per share) | $ / shares		$ 1.48				$ 8.265				$ 1.48	$ 8.265	$ 2.26
Income (loss) before income taxes		$ (50,957,000)	$ (12,263,000)	$ 18,874,000	$ 454,746,000	$ 67,530,000	$ 47,453,000	$ 196,352,000	$ 55,949,000	$ 410,400,000	$ 367,284,000	$ 136,271,000
Tax expense recorded from Tax Cuts and Jobs Act		17,000,000
Income tax expense									$ 53,000,000	0	48,181,000	796,000
Net operating loss carryforward		10,720,000				8,784,000				10,720,000	8,784,000	3,703,000
Amount that tax basis of net assets is less than reported amounts		1,700,000,000				$ 2,000,000,000				1,700,000,000	2,000,000,000	6,500,000,000
UK
Operating Loss Carryforwards [Line Items]
Income (loss) before income taxes										(4,000,000)	(4,000,000)	(15,000,000)
QCP
Operating Loss Carryforwards [Line Items]
Share price (usd per share) | $ / shares	$ 30.85
TRS
Operating Loss Carryforwards [Line Items]
Income (loss) before income taxes										(58,000,000)	$ (9,000,000)	$ (22,000,000)
Net operating loss carryforward		$ 42,000,000								$ 42,000,000