Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income, net of taxes	Retained Earnings	Treasury Stock
Balance at Dec. 31, 2014				$ 25
Comprehensive income:
Net income for the period	$ 31,804
Unrealized gain on available for sale marketable securities, net of taxes	(17)
Total comprehensive income	31,787
Balance at Jun. 30, 2015				8
Balance (in shares) at Dec. 31, 2015		73,793
Balance at Dec. 31, 2015	296,456	$ 738	$ 199,294	543	$ 106,886	$ (11,005)
Comprehensive income:
Net income for the period	37,386				37,386
Unrealized gain on available for sale marketable securities, net of taxes	1,133			1,133
Total comprehensive income	38,519
Exercise of stock options and other stock-based compensation, net of shares tendered (in shares)		245
Exercise of stock options and other stock-based compensation, net of shares tendered	4,777	$ 3	4,774
Tax benefit from equity compensation plans	897		897
Share-based compensation expense — stock options and restricted stock	1,878		1,878
Treasury shares issued for Deferred Compensation Plan funding and redemptions	534		513			21
Shares issued pursuant to Employee Stock Purchase Plan	2,067		1,696			371
Cash dividends	(26,451)				(26,451)
Shares issued pursuant to Dividend Reinvestment Plan	57		182			(125)
Shares issued pursuant to settlement (in shares)		113
Shares issued pursuant to settlement	4,000	$ 1	3,999
Balance (in shares) at Jun. 30, 2016		74,151
Balance at Jun. 30, 2016	$ 322,734	$ 742	$ 213,233	$ 1,676	$ 117,821	$ (10,738)