Acquisitions (Details) - USD ($)		3 Months Ended
	Feb. 01, 2017	Sep. 30, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill acquired		$ 916,000,000.0	$ 830,900,000
Green Tree Insurance Agency, Inc.
Business Acquisition [Line Items]
Acquisition percentage	100.00%
Initial cash payment	$ 125,000,000.0
Earn-out (up to)	25,000,000.0
Liabilities recorded in acquisition	10,400,000
Goodwill acquired	57,900,000
Tax-deductible goodwill	0
Adjusted intangible assets		(7,900,000)
Adjusted goodwill balance		$ 7,900,000
Green Tree Insurance Agency, Inc. | Agency relationships and renewal rights
Business Acquisition [Line Items]
Amortizable intangible assets	$ 77,500,000
Green Tree Insurance Agency, Inc. | Agency relationships and renewal rights | Minimum
Business Acquisition [Line Items]
Amortizable period	7 years
Green Tree Insurance Agency, Inc. | Agency relationships and renewal rights | Maximum
Business Acquisition [Line Items]
Amortizable period	16 years