Significant Accounting Policies - Estimated Useful Lives of Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Building and improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Computers and computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	1 year
Computers and computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Computer software | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Computer software | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Capitalized internal-use software development costs
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years