Summary of Significant Accounting Policies - Stockholders' Equity (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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)	0	0	1,942,200	2,070,600
Cost of shares repurchased	$ 0	$ 0	$ 52,400,000	$ 34,700,000
Remaining authorization under the program	$ 163,000,000		$ 163,000,000