CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - 9 months ended Sep. 30, 2016 - USD ($) $ in Thousands	Class A Common Stock	Paid-in Capital	Retained Earnings	Total
Balance at Dec. 31, 2015	$ 1,010	$ 2,227,376	$ 791,526	$ 3,019,912
Balance (in shares) at Dec. 31, 2015	102,582,669
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon exercise of options and vesting of restricted stock units		70		70
Issuance of common stock upon exercise of options and vesting of restricted stock units (in shares)	451,591
Stock-based compensation expense		12,342		12,342
Cash dividends (declared $0.15 per share)			(15,426)	(15,426)
Tax withholdings related to vesting of restricted stock units		(6,546)		(6,546)
Tax withholdings related to vesting of restricted stock units (in shares)	(190,951)
Net income			277,937	277,937
Balance at Sep. 30, 2016	$ 1,010	$ 2,233,242	$ 1,054,037	$ 3,288,289
Balance (in shares) at Sep. 30, 2016	102,843,309