Condensed Consolidated Statements of Changes In Stockholders' Equity - USD ($) $ in Thousands	Total	Capital Stock Preferred	Issued Common	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning Balance at Dec. 31, 2017	$ 168,730	$ 4	$ 6,715	$ 13,912	$ 167,129	$ (311)	$ (18,719)
Comprehensive income:
Net income	8,927				8,927
Other comprehensive loss	(13)					(13)
Dividends and dividend equivalents net of estimated forfeitures	(1,374)				(1,374)
Share-based compensation	1,052			1,052
Stock shares awarded, forfeited, or vested	139			(981)			1,120
Purchase of treasury stock for tax withholding on share-based compensation	(2,073)						(2,073)
Ending Balance at Mar. 31, 2018	175,388	4	6,715	13,983	174,682	(324)	(19,672)
Beginning Balance at Dec. 31, 2017	168,730	4	6,715	13,912	167,129	(311)	(18,719)
Comprehensive income:
Net income	16,454
Ending Balance at Jun. 30, 2018	182,360	4	6,715	14,484	180,835	(283)	(19,395)
Beginning Balance at Mar. 31, 2018	175,388	4	6,715	13,983	174,682	(324)	(19,672)
Comprehensive income:
Net income	7,527				7,527
Other comprehensive loss	41					41
Dividends and dividend equivalents net of estimated forfeitures	(1,374)				(1,374)
Share-based compensation	501			501
Stock shares awarded, forfeited, or vested	277			0			277
Ending Balance at Jun. 30, 2018	182,360	4	6,715	14,484	180,835	(283)	(19,395)
Comprehensive income:
Adjustment related to Accounting Standards Update 2018-02 adoption	0				(69)	69
Beginning Balance at Dec. 31, 2018	201,441	4	6,715	15,375	198,914	(164)	(19,403)
Comprehensive income:
Net income	9,720				9,720
Other comprehensive loss	14					14
Dividends and dividend equivalents net of estimated forfeitures	(1,714)				(1,714)
Share-based compensation	1,031			1,031			0
Stock shares awarded, forfeited, or vested	94			(3,770)			3,864
Purchase of treasury stock for tax withholding on share-based compensation	(5,467)						(5,467)
Ending Balance at Mar. 31, 2019	205,119	4	6,715	12,636	206,851	(81)	(21,006)
Beginning Balance at Dec. 31, 2018	201,441	4	6,715	15,375	198,914	(164)	(19,403)
Comprehensive income:
Net income	17,631
Ending Balance at Jun. 30, 2019	212,442	4	6,715	13,117	213,049	(97)	(20,346)
Beginning Balance at Mar. 31, 2019	205,119	4	6,715	12,636	206,851	(81)	(21,006)
Comprehensive income:
Net income	7,911				7,911
Other comprehensive loss	(16)					(16)
Dividends and dividend equivalents net of estimated forfeitures	(1,713)				(1,713)
Share-based compensation	481			481			0
Stock shares awarded, forfeited, or vested	660			0			660
Ending Balance at Jun. 30, 2019	$ 212,442	$ 4	$ 6,715	$ 13,117	$ 213,049	$ (97)	$ (20,346)