Equity - Additional Information (Details) - USD ($)	1 Months Ended	2 Months Ended	12 Months Ended
	Feb. 28, 2018	Feb. 26, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 29, 2016
Stockholders Equity Note [Line Items]
Share repurchases			$ 9,187,000	$ 25,107,000	$ 88,785,000
Share Repurchase Plan, February 2016
Stockholders Equity Note [Line Items]
Stock repurchase program, authorized amount						$ 100,000,000
Share repurchased during period (in shares)			610,342
Share repurchases			$ 9,000,000
Stock repurchase program, remaining authorized repurchase amount			$ 77,000,000
Share Repurchase Plan, February 2016 | Subsequent Event
Stockholders Equity Note [Line Items]
Share repurchased during period (in shares)		1,040,829
Share repurchases		$ 16,000,000
Share Repurchase Plan, February 2018 | Subsequent Event
Stockholders Equity Note [Line Items]
Stock repurchase program, authorized amount	$ 100,000,000
Increase in authorized repurchase amount	$ 39,000,000
Stock repurchase program, remaining authorized repurchase amount		$ 100,000,000
Convertible debt securities
Stockholders Equity Note [Line Items]
Securities excluded in the calculation of diluted earnings per share			0	0	21,292,309
Equity awards
Stockholders Equity Note [Line Items]
Securities excluded in the calculation of diluted earnings per share			5,843	0	103,253