(Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Jan. 01, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent										21.00%	35.00%	35.00%
Income Tax Expense (Benefit)		$ (596)	$ 12,671	$ (1,553)	$ 2,542	$ 35,069	$ (339)	$ 1,524	$ (1,113)	$ 13,064	$ 35,141	$ 3,514
Tax Cuts And Jobs Act Of 2017 Reclassification From AOCI To Retained Earnings Tax Effect	$ 4,700
Effective Income Tax Rate Reconciliation, Percent										652.60%	(1176.90%)	64.10%
Deferred Tax Liability, Tax Valuation Allowance		0				$ 0				$ 0	$ 0
Operating Loss Carryforwards		900								$ 900
Operating Loss Carryforwards, Expiration Date										Dec. 31, 2031
Deferred Tax Assets, Capital Loss Carryforwards		$ 0								$ 0
Unrecognized Tax Benefits, Excluding Bond Premium Amortization, Decrease Resulting from Prior Period Tax Position										$ 50,800
Eligibility Date to File with Consolidated Federal Income Tax Return										Dec. 31, 2020