Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2012	$ 751,186	$ 271,335	$ 463,860	$ 15,991
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	86,136	0	86,136	0
Other comprehensive loss, net of tax	(32,032)	0	0	(32,032)
Common stock transactions:
Common shares purchased and retired	448	(448)	0	0
Common shares issued	543	543	0	0
Non-vested common shares issued	0	0	0	0
Non-vested common shares forfeited or canceled	0	0	0	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	9,271	9,271	0	0
Tax benefit of stock-based compensation	1,898	1,898	0	0
Stock-based compensation expense	2,936	2,936	0	0
Cash dividends declared:
Common (per share)	(17,909)	0	(17,909)	0
Ending Balance at Dec. 31, 2013	801,581	285,535	532,087	(16,041)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	84,401	0	84,401	0
Other comprehensive loss, net of tax	13,507	0	0	13,507
Common stock transactions:
Common shares purchased and retired	(9,739)	(9,739)	0	0
Common shares issued	35,674	35,674	0	0
Non-vested common shares issued	0	0	0	0
Non-vested common shares forfeited or canceled	0	0	0	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	6,299	6,299	0	0
Tax benefit of stock-based compensation	2,193	2,193	0	0
Stock-based compensation expense	3,634	3,634	0	0
Cash dividends declared:
Common (per share)	(28,626)	0	(28,626)	0
Ending Balance at Dec. 31, 2014	908,924	323,596	587,862	(2,534)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	86,795	0	86,795	0
Other comprehensive loss, net of tax	2,940	0	0	2,940
Common stock transactions:
Common shares purchased and retired	(20,647)	(20,647)	0	0
Common shares issued	0	0	0	0
Non-vested common shares issued	0	0	0	0
Non-vested common shares forfeited or canceled	0	0	0	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	3,369	3,369	0	0
Tax benefit of stock-based compensation	1,443	1,443	0	0
Stock-based compensation expense	3,959	$ 3,959	0	0
Cash dividends declared:
Common (per share)	(36,290)		(36,290)	0
Ending Balance at Dec. 31, 2015	$ 950,493	$ 311,720	$ 638,367	$ 406