CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - 6 months ended Jun. 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		47		47
Issuance of common stock upon exercise of options and vesting of restricted stock units (in shares)	450,743
Stock-based compensation expense		7,740		7,740
Cash dividends (declared $0.15 per share)			(10,285)	(10,285)
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			184,661	184,661
Balance at Jun. 30, 2016	$ 1,010	$ 2,228,617	$ 965,902	$ 3,195,529
Balance (in shares) at Jun. 30, 2016	102,842,461