CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS’ EQUITY - USD ($) shares in Thousands, $ in Thousands		Total	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Equity, beginning of period (in shares) at Dec. 31, 2016			36,988
Equity, beginning of period at Dec. 31, 2016		$ 430,482	$ 372	$ 382,961	$ 49,127	$ (725)	$ (1,253)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		31,517			31,517
Other comprehensive income (loss)		(1,216)				(1,216)
Issuance of common stock in connection with exercise of stock options (in shares)			286
Issuance of common stock in connection with exercise of stock options		470	$ 1	469
Stock-based compensation expense		1,058		1,058
Equity, end of period (in shares) at Sep. 30, 2017			37,274
Equity, end of period at Sep. 30, 2017		462,311	$ 373	384,488	80,644	(1,941)	(1,253)
Equity, beginning of period (in shares) at Dec. 31, 2017			37,103
Equity, beginning of period at Dec. 31, 2017		463,795	$ 373	387,891	83,263	(6,479)	(1,253)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification upon adoption of new accounting standards | Accounting Standards Update 2018-02	[1]	0			1,396	(1,396)
Reclassification upon adoption of new accounting standards | Accounting Standards Update 2016-01	[1]	(63)			(299)	236
Net income		41,380
Other comprehensive income (loss)		(13,031)				(13,031)
Issuance of common stock in connection with exercise of stock options (in shares)			265
Issuance of common stock in connection with exercise of stock options		2,884	$ 2	2,882
Stock-based compensation expense		2,703		2,703
Cash dividend declared, $0.10 per share		(7,464)			(7,464)
Equity, end of period (in shares) at Sep. 30, 2018			37,368
Equity, end of period at Sep. 30, 2018		$ 490,204	$ 375	$ 393,476	$ 118,276	$ (20,670)	$ (1,253)

[1] Adoption of Accounting Standards Updates 2018-02 and 2016-01. See Notes 3 and 14 to interim condensed consolidated financial statements for additional information.