Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK [Member]	CAPITAL SURPLUS [Member]	RETAINED EARNINGS [Member]	ACCUMULATED OTHER COMPREHENSIVE INCOME [Member]
Balance at beginning of period at Dec. 31, 2013		$ 15,334	$ 88,803	$ 448,953	$ 3,907
Balance at beginning of period, Shares at Dec. 31, 2013		15,333,622
Shares issued, Value		$ 170	4,742
Shares issued, Shares		170,891
Net income	$ 63,887			63,887
Other comprehensive (loss) gain, net of tax of $903, $1,682 and $(541), respectively	286				286
Tax effect of stock options			1,620
Dividends on common stock				(20,064)
Stock-based compensation arrangements			1,676
Balance at end of period at Dec. 31, 2014	$ 609,314	$ 15,504	96,841	492,776	4,193
Balance at end of period, Shares at Dec. 31, 2014	15,504,513	15,504,513
Shares issued, Value		$ 121	3,116
Shares issued, Shares		121,380
Net income	$ 66,170			66,170
Other comprehensive (loss) gain, net of tax of $903, $1,682 and $(541), respectively	(2,666)				(2,666)
Tax effect of stock options			1,191
Dividends on common stock				(21,799)
Stock-based compensation arrangements			1,717
Shares acquired and canceled, Value		$ (28)		(1,626)
Shares acquired and canceled, Shares		(28,447)
Balance at end of period at Dec. 31, 2015	$ 655,510	$ 15,597	102,865	535,521	1,527
Balance at end of period, Shares at Dec. 31, 2015	15,597,446	15,597,446
Shares issued, Value		$ 314	9,519
Shares issued, Shares		313,489
Net income	$ 70,674			70,674
Other comprehensive (loss) gain, net of tax of $903, $1,682 and $(541), respectively	(1,433)				(1,433)
Tax effect of stock options			3,521
Dividends on common stock				(23,124)
Stock-based compensation arrangements			1,636
Shares acquired and canceled, Value		$ (100)		(5,423)
Shares acquired and canceled, Shares		(100,000)
Balance at end of period at Dec. 31, 2016	$ 711,094	$ 15,811	$ 117,541	$ 577,648	$ 94
Balance at end of period, Shares at Dec. 31, 2016	15,810,935	15,810,935