Net Income Per Share Reconciliation of Weighted Average Common Shares Outstanding (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding (basic) (in shares)	175,764	174,597	175,535	174,375
Impact of common stock equivalents (in shares)	1,080	935	1,171	1,179
Weighted average shares outstanding (diluted) (in shares)	176,844	175,532	176,706	175,554