CONDENSED CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands		Total		Capital Stock	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		$ 36,370
Other comprehensive income (loss)	[1]	6,721
Balance, End of Period at Sep. 30, 2016							(81,737)
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		73,460
Other comprehensive income (loss)		22,942	[2]				22,942
Stock options exercised		1,926		53	1,873
Stock issued to directors		0		15	(15)
Shares issued for employees stock purchase plan		895		15	880
Shares issued for vested restricted stock units, net of cancellations for tax withholding		(5,145)		114	(5,259)
Cumulative-effect adjustment of change in accounting for share-based compensation		12,732				12,732
Stock-based compensation expense		8,508			8,508
Balance, End of Period at Sep. 30, 2017		$ 751,104		$ 18,218	$ 124,665	$ 677,541	$ (69,320)

[1] Net of taxes of $58 and $5 for the pension plans and postretirement benefits and unrealized gain (loss) on derivatives, respectively.

[2] Net of taxes of $38 and $(151) for the pension plans and postretirement benefits and unrealized gain (loss) on derivatives, respectively.