Earnings per Share Share Repurchase (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Oct. 25, 2018	Sep. 30, 2015
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	111,289	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		$ 72.35
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	$ 73.94
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 335,000
Class A Common Shares [Member] | Share Repurchase Program 1 [Member]
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased		793,000
Class A Common Shares [Member] | Share Repurchase Program 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	65,000