Consolidated Statements of Stockholders' Equity - 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	$ 48,890
Unrealized gain on available for sale marketable securities, net of taxes	181
Total comprehensive income	49,071
Balance at Sep. 30, 2015				206
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	57,097				57,097
Unrealized gain on available for sale marketable securities, net of taxes	765			765
Total comprehensive income	57,862
Exercise of stock options and other stock-based compensation, net of shares tendered (in shares)		284
Exercise of stock options and other stock-based compensation, net of shares tendered	5,600	$ 3	5,597
Tax benefit from equity compensation plans	1,540		1,540
Share-based compensation expense — stock options and restricted stock	2,810		2,810
Treasury shares issued for Deferred Compensation Plan funding and redemptions	534		325			209
Shares issued pursuant to Employee Stock Purchase Plan	2,067		1,696			371
Cash dividends	(39,849)				(39,849)
Shares issued pursuant to Dividend Reinvestment Plan	84		270			(186)
Shares issued pursuant to settlement (in shares)		113
Shares issued pursuant to settlement	4,000	$ 1	3,999
Balance (in shares) at Sep. 30, 2016		74,187
Balance at Sep. 30, 2016	$ 331,104	$ 742	$ 215,531	$ 1,308	$ 124,134	$ (10,611)