Summary of Significant Accounting Policies (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Authorized amount from Board of Directors for share repurchase						$ 250,000,000
Number of shares repurchased (in shares)		1,942,200	0	1,942,200	2,070,600
Cost of shares repurchased		$ 52,400,000	$ 0	$ 52,400,000	$ 34,700,000
Shares repurchased settled in subsequent month	$ 10,500,000
Remaining authorization under the program	$ 163,000,000	$ 163,000,000		$ 163,000,000