CONDENSED CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Capital Stock/Capital Shares	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance, Beginning of Period at Dec. 31, 2015					$ (88,458)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 20,305
Other comprehensive income (loss)	5,279
Balance, End of Period at Jun. 30, 2016					(83,179)
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	47,928
Other comprehensive income (loss)	16,772				16,772
Stock options exercised	1,905	50	1,855
Stock issued to directors	0	12	(12)
Shares issued for employees stock purchase plan	422	8	414
Shares issued for vested restricted stock units, net of cancellations for tax withholding	(2,617)	70	(2,687)
Cumulative-effect adjustment of change in accounting for share-based compensation	12,732			12,732
Stock-based compensation expense	5,327		5,327
Balance, End of Period at Jun. 30, 2017	$ 718,255	$ 18,161	$ 123,575	$ 652,009	$ (75,490)