Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Dec. 31, 2017	$ 544,864	$ 3,427	$ 165,979	$ 429,826	$ (12,140)	$ (42,228)
Balance (in shares) at Dec. 31, 2017		34,270,975
Impact of change in accounting policy at Dec. 31, 2017	16,219			16,219
Adjusted balance at Dec. 31, 2017	561,083	$ 3,427	165,979	446,045	(12,140)	(42,228)
Net income	24,058			24,058
Other comprehensive income (loss)	3,224					3,224
Exercise of stock options	2,722	$ 11	2,711
Exercise of stock options (in shares)		112,669
Stock option expense	1,039		1,039
Restricted stock expense	6		6
Performance share expense	605		605
Balance at Mar. 31, 2018	592,737	$ 3,438	170,340	470,103	(12,140)	(39,004)
Balance (in shares) at Mar. 31, 2018		34,383,644
Balance at Dec. 31, 2018	$ 653,727	$ 3,487	182,691	538,463	(10,777)	(60,137)
Balance (in shares) at Dec. 31, 2018	34,870,124	34,870,124
Net income	$ 10,409			10,409
Other comprehensive income (loss)	(6,533)					(6,533)
Exercise of stock options	65		65
Exercise of stock options (in shares)		4,000
Issuance of performance shares		$ 5	(5)
Issuance of performance shares (in shares)		46,000
Stock option expense	1,062		1,062
Restricted stock expense	96		96
Performance share expense	501		501
Balance at Mar. 31, 2019	$ 659,327	$ 3,492	$ 184,410	$ 548,872	$ (10,777)	$ (66,670)
Balance (in shares) at Mar. 31, 2019	34,920,124	34,920,124