CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 3 months ended Mar. 31, 2017 - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2016	$ 951	$ 2,763,452	$ (722,359)	$ 945	$ 2,042,989
Balance, shares at Dec. 31, 2016	95,124
Increase (Decrease) in Stockholders' Equity
Dividends			3		3
Dividends in Excess of Retained Earnings		(7,609)			(7,609)
Net income			130,972		130,972
Unrealized change in fair value of investments, net of tax				402	402
Issuance of restricted stock awards, shares	5
Common stock reacquired and retired		(938)			(938)
Common stock reacquired and retired, shares	(8)
Restricted stock forfeited and retired, shares	(5)
Exercise of stock options		36			36
Exercise of stock options, shares	1
Stock-based compensation		11,988			11,988
Cumulative effect adjustment of adopting ASU 2016-09		4,393	28,739		33,132
Other		(26)			(26)
Balance at Mar. 31, 2017	$ 951	$ 2,771,296	$ (562,645)	$ 1,347	$ 2,210,949
Balance, shares at Mar. 31, 2017	95,117