Summary of Significant Accounting Policies (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) Segment	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)
Description of Business [Abstract]
Number of reportable segments | Segment	1
Recently Adopted Accounting Pronouncements [Abstract]
Corporate income tax rate	21.00%	35.00%
ASU 2016-01 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Cumulative-effect adjustment to reclassify unrealized gains on equity securities after tax		$ 0
ASU 2016-02 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Right-of-use asset	$ 210
Lease liability	$ 210
ASU 2018-02 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Cumulative-effect adjustment to reclassify unrealized gains on equity securities after tax		0
Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Cumulative-effect adjustment to reclassify unrealized gains on equity securities before tax		(71,012)
Cumulative-effect adjustment to reclassify unrealized gains on equity securities after tax		(46,157)
Other Comprehensive Income (Loss) [Member] | ASU 2018-02 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Cumulative-effect adjustment to reclassify unrealized gains on equity securities after tax		117	$ 117
Retained Earnings [Member] | ASU 2016-01 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Cumulative-effect adjustment to reclassify unrealized gains on equity securities before tax		71,012
Cumulative-effect adjustment to reclassify unrealized gains on equity securities after tax		46,157
Retained Earnings [Member] | ASU 2018-02 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Cumulative-effect adjustment to reclassify unrealized gains on equity securities after tax		$ (117)	$ (117)