Stockholders' Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Issuance and vesting of restricted stock (in shares)	1,598,000	1,426,000	1,385,000
Common stock issued through stock option exercise (in shares)	226,845	202,000	183,000
Unvested restricted stock forfeitures (in shares)	27,000	82,000	304,000
Stock repurchases for satisfaction of tax obligations (in shares)	280,000	232,000	183,000
Maximum amount authorized to be repurchased under the common stock repurchase program	$ 500,000,000.0
Number of shares repurchased under the program (in shares)	0	0	1,032,334
Repurchase of common shares			$ 13,600,000
Repurchase program available capacity	$ 185,200,000