Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Authorized stock repurchase, amount	$ 500,000		$ 500,000
Repurchase and retirement of common stock, Shares	0	12,402	0	12,402
Average share price		$ 74.28		$ 74.28
Repurchase and retirement of common stock		$ 921		$ 921
Remaining authorized stock repurchase, amount	$ 416,559		$ 416,559
Common Stock [Member] | Common Class A [Member]
Repurchase and retirement of common stock, Shares		12,000		12,000
Additional Paid-In Capital [Member]
Repurchase and retirement of common stock		$ 122		$ 122
Accumulated Deficit [Member]
Repurchase and retirement of common stock		$ 799		$ 799