Earnings per Share Share Repurchase (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Oct. 25, 2018	Sep. 30, 2015
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	107	111,289	1,873,170	832,232
Share Repurchase Program 1 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount								$ 300,000
Average stock price of Class A Common Stock repurchased			$ 72.04			$ 72.14
Stock Repurchase Program, Remaining Authorized Repurchase Amount							$ 0
Share Repurchase Program 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount							$ 500,000
Average stock price of Class A Common Stock repurchased	$ 0				$ 73.94
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 335,000				$ 335,000
Class A Common Shares [Member] | Share Repurchase Program 1 [Member]
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased			1,873,000			2,666,000
Class A Common Shares [Member] | Share Repurchase Program 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	0				65,000