Share Repurchase Programs - Schedule of Share Repurchase Program (Details) - USD ($)	6 Months Ended		12 Months Ended	47 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jun. 30, 2018	Feb. 16, 2017
Equity, Class of Treasury Stock [Line Items]
Number of Shares			2,519,927	15,737,691
Average Repurchase Price Per Share			$ 36.06	$ 34.12
Amount spent, share repurchase programs	$ 29,355,000	$ 38,567,000	$ 90,868,000
2017 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized	300,000,000			$ 300,000,000	$ 300,000,000
Amount spent excluding commissions, share repurchase programs	$ 106,050,000
Number of Shares	986,935		2,136,237
Average Repurchase Price Per Share	$ 29.74		$ 35.95
Amount spent, share repurchase programs	$ 29,355,000		$ 76,788,000
2016 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized	200,000,000			$ 200,000,000
Amount spent excluding commissions, share repurchase programs	$ 104,366,000
Share repurchase, remaining amount authorized					$ 95,634,000
Number of Shares			383,690
Average Repurchase Price Per Share			$ 36.70
Amount spent, share repurchase programs			$ 14,080,000