Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Non-Controlling Interest [Member]
Balances at Dec. 31, 2013	$ 632,530	$ 737	$ 143,017	$ 488,978	$ (3,672)	$ 0	$ 3,470
Net income	51,746	0	0	51,746	0	0	0
Earnings attributable to noncontrolling interest	0	0	0	16	0	0	(16)
Total other comprehensive income (loss)	13,678	0	0	0	13,678	0	0
Common stock dividends paid	(16,606)	0	0	(16,606)	0	0	0
Issuance of common stock for exercise of stock options	1,572	2	1,570	0	0	0	0
Excess tax benefit on stock-based compensation	1,373	0	1,373	0	0	0	0
Stock-based compensation expense	3,050	0	3,050	0	0	0	0
Forfeiture of unvested restricted common stock	0	0	0	0	0	0	0
Issuance of common stock for acquisition	166,315	58	166,257	0	0	0	0
Balances at Jun. 30, 2014	853,658	797	315,267	524,134	10,006	0	3,454
Balances at Dec. 31, 2014	911,842	799	324,354	571,454	14,132	(2,349)	3,452
Net income	84,722	0	0	84,722	0	0	0
Earnings attributable to noncontrolling interest	0	0	0	(52)	0	0	52
Total other comprehensive income (loss)	(6,064)	0	0	0	(6,064)	0	0
Common stock dividends paid	(22,126)	0	0	(22,126)	0	0	0
Issuance of common stock for exercise of stock options	997	1	996	0	0	0	0
Issuance of unvested restricted common stock	0	2	(2,351)	0	0	2,349	0
Excess tax benefit on stock-based compensation	791	0	791	0	0	0	0
Stock-based compensation expense	4,220	0	4,220	0	0	0	0
Forfeiture of unvested restricted common stock	0	0	0	0	0	0	0
Issuance of common stock to non-employee directors	0	0	0	0	0	0	0
Issuance of common stock for acquisition	238,376	66	238,310	0	0	0	0
Balances at Jun. 30, 2015	$ 1,212,758	$ 868	$ 566,320	$ 633,998	$ 8,068	$ 0	$ 3,504