Related Party Transactions - Underwritten Public Offering (Details) - shares	May 11, 2018	Mar. 15, 2018	Feb. 15, 2018	Nov. 21, 2017	Nov. 17, 2017	May 12, 2017
Related Party Transaction [Line Items]
Issuance of common stock (in shares)	12,100,000	8,000,000	8,000,000	800,000	7,000,000	5,800,000
Purchases of treasury stock (share)	0	1,000,000	2,000,000		2,000,000	0
THL and its affiliates [Member]
Related Party Transaction [Line Items]
Investment Owned, Balance, Shares	0	12,100,000	20,100,000		28,100,000	35,100,000