Related-Party Transactions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transactions
Premiums paid related to agreements	$ 0
Revenue from related party	65,700,000		$ 142,200,000
Expenses from business transactions with unconsolidated affiliates	100,000	$ 100,000
Accounts receivable from affiliated entities	54,200,000	100,000
Accounts payable to affiliated entities		100,000
Long-term payables with affiliated entities	800,000	800,000
James R Crane | Crane Capital Group Inc
Related Party Transactions
Accounts payable to affiliated entities	800,000	1,000,000
Amount paid to related party for services provided	14,600,000	$ 23,500,000	$ 33,700,000
Management
Related Party Transactions
Premium payments to date related to life insurance policies	6,600,000
Cash surrender value included in other long-term assets	$ 6,000,000