Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Basis differences related to financial derivatives	$ 100,099	$ 51,177
Unrealized losses on securities	0	2,805
Allowance for losses	3,690	2,650
Unrealized losses on cash flow hedges	6,065	1,491
Stock-based compensation	1,027	571
Capital loss carryforwards and other-than-temporary impairment	86	86
Valuation allowance	(86)	(86)
Other	341	88
Total deferred tax assets	112,242	59,601
Deferred tax liability:
Basis differences related to hedged items	91,460	42,940
Unrealized gains on securities	2,364	0
Other	97	151
Total deferred tax liability	93,921	43,091
Net deferred tax asset	18,321	16,510
Capital Loss Carryforward
Deferred tax assets:
Compensation and benefits	$ 1,020	$ 819