Summary of Significant Accounting Policies - Finite-lived and Indefinite-lived Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Other Intangible Assets
Goodwill	$ 1,008,097	$ 989,685	$ 911,942
Other intangible assets, net	$ 422,606	$ 435,494
Land Improvements
Estimated useful lives of property and equipment
Useful lives	15 years
Building And Building Improvements | Minimum
Estimated useful lives of property and equipment
Useful lives	5 years
Building And Building Improvements | Maximum
Estimated useful lives of property and equipment
Useful lives	31 years
Furniture, Fixtures and Equipment | Minimum
Estimated useful lives of property and equipment
Useful lives	3 years
Furniture, Fixtures and Equipment | Maximum
Estimated useful lives of property and equipment
Useful lives	31 years