Consolidated Statement of Stockholders' Equity - 3 months ended Mar. 31, 2018 - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in-Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance, shares at Dec. 31, 2017		25,515
Beginning balance at Dec. 31, 2017	$ 1,124,282	$ 255	$ 291,461	$ 1,246,323	$ (123,226)	$ (290,531)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	35,814	0	0	35,814	0	0
Other comprehensive income (loss), net of tax	17,276	0	0	0	17,276	0
Stock Issued During Period, Value, Treasury Stock Reissued	(9,199)	$ 0	0	0	0	(9,199)
Stock Issued During Period, Shares, Employee Stock Purchase Plans		12
Stock Issued During Period, Value, Employee Stock Purchase Plan	(1,638)	$ 0	10,846	0	0	(9,208)
Stock-based compensation	5,629	0	5,629	0	0	0
Cash dividends	(5,482)	$ 0	0	(5,482)	0	0
Ending balance, shares at Mar. 31, 2018		25,527
Ending balance at Mar. 31, 2018	$ 1,178,079	$ 255	286,244	$ 1,288,052	$ (105,950)	$ (290,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation