CONDENSED CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Capital Stock/Capital Shares	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance, Beginning of Period at Dec. 31, 2015					$ (88,458)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 14,928
Other comprehensive income (loss)	10,967
Balance, End of Period at Mar. 31, 2016					(77,491)
Balance, Beginning of Period at Dec. 31, 2016	635,786	$ 18,021	$ 118,678	$ 591,349	(92,262)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27,032			27,032
Other comprehensive income (loss)	4,054				4,054
Stock options exercised	765	22	743
Shares issued for employees stock purchase plan	422	8	414
Shares issued for vested restricted stock units, net of cancellations for tax withholding	(2,572)	70	(2,642)
Cumulative-effect adjustment of change in accounting for share-based compensation	12,732			12,732
Stock-based compensation expense	1,020		1,020
Balance, End of Period at Mar. 31, 2017	$ 679,239	$ 18,121	$ 118,213	$ 631,113	$ (88,208)