Financial Statements Restatement (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended
	Jul. 01, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Federal income tax expense (benefit)		$ 86			$ 12,671			$ 7,138	$ 13,660
Net income (loss)		2,046	$ (4,565)	$ (3,802)	(7,109)	$ (2,558)	$ 37	(6,321)	(9,630)
Comprehensive income (loss)		24,567	24,411	23,078	(9,143)	(12,229)	(14,067)	72,056	(35,439)
Stockholders' Equity, Balance at January 1, 2018											$ 223,513
Novation Date	Jul. 01, 2018
Retained Earnings (Accumulated Deficit)		(75,920)			(68,167)			(75,920)	(68,167)	$ (69,599)
Stockholders' equity		261,342	236,432	211,894	188,384	197,430	209,446	261,342	188,384	187,733		$ 223,513
Deferred federal income tax benefit								560	59,329
Federal income tax receivable								6,580	(45,678)
Net cash provided by operating activities								50,913	65,235
Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Federal income tax expense (benefit)					20,316				21,305
Net income (loss)					(14,754)				(17,275)
Comprehensive income (loss)					(16,788)				(43,084)
Retained Earnings (Accumulated Deficit)					(75,812)				(75,812)
Stockholders' equity					180,739				180,739
Deferred federal income tax benefit									67,040
Federal income tax receivable									(45,744)
Net cash provided by operating activities									65,235
Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Federal income tax expense (benefit)					(7,645)				(7,645)
Net income (loss)					7,645				7,645
Comprehensive income (loss)					7,645				7,645
Retained Earnings (Accumulated Deficit)					7,645				7,645
Stockholders' equity					7,645				7,645
Deferred federal income tax benefit									(7,711)
Federal income tax receivable									66
Net cash provided by operating activities									0
Accumulated deficit [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)		2,046	(4,565)	(3,802)	(7,109)	(2,558)	37	(6,321)	(9,630)
Comprehensive income (loss)		2,046	(4,565)	(3,802)	(7,109)	(2,558)	37
Stockholders' Equity, Balance at January 1, 2018						197,430					$ (58,537)
Stockholders' equity		$ (75,920)	$ (77,966)	$ (73,401)	$ (68,167)	(61,058)	$ (58,500)	$ (75,920)	$ (68,167)	$ (69,599)		$ (54,375)
Accumulated deficit [Member] | Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' Equity, Balance at January 1, 2018						197,430
Accumulated deficit [Member] | Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' Equity, Balance at January 1, 2018						$ 0
Common Class A [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Basic and diluted earnings (loss) per share (in dollars per share)		$ 0.04			$ (0.14)			$ (0.13)	$ (0.19)
Common Class A [Member] | Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Basic and diluted earnings (loss) per share (in dollars per share)					(0.30)				(0.35)
Common Class A [Member] | Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Basic and diluted earnings (loss) per share (in dollars per share)					0.16				0.16
Common Class B [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Basic and diluted earnings (loss) per share (in dollars per share)		$ 0.02			(0.07)			$ (0.06)	(0.10)
Common Class B [Member] | Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Basic and diluted earnings (loss) per share (in dollars per share)					(0.14)				(0.17)
Common Class B [Member] | Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Basic and diluted earnings (loss) per share (in dollars per share)					$ 0.07				$ 0.07