Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss), net of taxes	Retained Earnings	Treasury Stock
Beginning balance at Dec. 31, 2015				$ 543
Comprehensive income:
Net income for the period	$ 18,626
Unrealized gain on available for sale marketable securities, net of taxes	555
Total comprehensive income	19,181
Ending balance at Mar. 31, 2016				1,098
Balance (in shares) at Dec. 31, 2016		74,204
Beginning balance at Dec. 31, 2016	338,842	$ 742	$ 217,664	(319)	$ 130,940	$ (10,185)
Comprehensive income:
Net income for the period	22,017				22,017
Unrealized gain on available for sale marketable securities, net of taxes	479			479
Total comprehensive income	22,496
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)		219
Exercise of stock options and other stock-based compensation, net of shares tendered for payment	4,687	$ 2	4,685
Share-based compensation expense — stock options, restricted stock and restricted stock units	1,459		1,459
Treasury shares issued for Deferred Compensation Plan funding and redemptions	502		495			7
Shares issued pursuant to Employee Stock Plan	2,091		1,752			339
Cash dividends	(13,624)				(13,624)
Shares issued pursuant to Dividend Reinvestment Plans	24		20			4
Balance (in shares) at Mar. 31, 2017		74,423
Ending balance at Mar. 31, 2017	$ 356,477	$ 744	$ 226,075	$ 160	$ 139,333	$ (9,835)