CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - 6 months ended Jun. 30, 2017 - USD ($) $ in Thousands	Class A Common Stock	Paid-in Capital	Retained Earnings	Total
Balance at Dec. 31, 2016	$ 1,010	$ 2,237,866	$ 1,143,311	$ 3,382,187
Balance (in shares) at Dec. 31, 2016	102,844,477
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options and warrants	$ 2	1,695		1,697
Issuance of common stock upon vesting of restricted stock units and upon exercise of options and warrants (in shares)	505,104
Stock-based compensation expense		9,077		9,077
Cash dividends (declared $0.15 per share)			(15,477)	(15,477)
Tax withholding related to vesting of restricted stock units and exercise of stock options		(5,600)		(5,600)
Tax withholding related to vesting of restricted stock units and exercise of stock options (in shares)	(138,147)
Net income			185,862	185,862
Balance at Jun. 30, 2017	$ 1,012	$ 2,243,038	1,314,154	3,558,204
Balance (in shares) at Jun. 30, 2017	103,211,434
Increase (Decrease) in Shareholders' Equity
Cumulative effect adjustment upon adoption of ASU 2016-09 | Accounting Standards Update 2016 - 09			$ 458	$ 458