Inventories - Schedule of Changes in Accounting Principles (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales	$ 97,290	$ 102,437	$ 197,349	$ 205,063
Net income	$ 5,377	$ 13,554	$ 20,305	$ 27,197
Basic earnings per share (in dollars per share)	$ 0.30	$ 0.73	$ 1.13	$ 1.47
Diluted earnings per share (in dollars per share)	$ 0.29	$ 0.71	$ 1.11	$ 1.43
As Originally Reported Under LIFO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		$ 102,509		$ 205,205
Net income		$ 13,540		$ 27,167
Basic earnings per share (in dollars per share)		$ 0.73		$ 1.46
Diluted earnings per share (in dollars per share)		$ 0.71		$ 1.43
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		$ (72)		$ (142)
Net income		$ 14		$ 30
Basic earnings per share (in dollars per share)		$ 0.00		$ 0.00
Diluted earnings per share (in dollars per share)		$ 0.00		$ 0.00