Equity method investment - Financial Position and Results of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Assets	$ 33,824,931		$ 33,824,931		$ 27,805,496
Liabilities	29,037,623		29,037,623		23,449,748
Liabilities and Equity	33,824,931		33,824,931		27,805,496
Bankers Healthcare Group, LLC
Schedule of Equity Method Investments [Line Items]
Assets	1,249,530		1,249,530		840,398
Liabilities	1,006,462		1,006,462		641,037
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	243,068		243,068		199,361
Liabilities and Equity	1,249,530		1,249,530		$ 840,398
Revenues	128,510	$ 108,770	319,244	$ 279,569
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 51,459	$ 61,364	$ 121,604	$ 156,064