Basis of Presentation and Significant Accounting Policies Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Preferred Stock, Shares Outstanding		0	0
Stockholders' Equity Attributable to Noncontrolling Interest		$ 59,968	$ 41,150
Operating Lease, Liability		$ 29,664	$ 15,000
Preferred Stock, Shares Issued		0	0
Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
Derivative [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 2,900
Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
Derivative [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(2,900)
Deferred Income Tax Charge [Member] | Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
Derivative [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 590
Ambac Assurance Corporation [Member]
Derivative [Line Items]
Preferred Stock, Shares Outstanding		5,501	4,115
Preferred Stock, Liquidation Preference, Value		$ 137,525	$ 102,875
Preferred Stock, Shares Issued		1,386