Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock Including APIC [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2013	$ 751,872	$ 364,549	$ 393,681	$ (6,358)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	54,974	0		(3,718)
Net income	58,692		58,692
Dividends on common stock	(50,093)	0	(50,093)	0
Tax expense from employee stock plans	(117)	(117)	0	0
Stock-based compensation	1,646	1,646	0	0
Shares issued pursuant to equity based plans	9,039	9,039	0	0
Balance at Dec. 31, 2014	767,321	375,117	402,280	(10,076)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	56,617	0		2,914
Net income	53,703		53,703
Dividends on common stock	(50,993)	0	(50,993)	0
Tax expense from employee stock plans	(118)	(118)	0	0
Stock-based compensation	3,277	3,277	0	0
Shares issued pursuant to equity based plans	4,868	4,868	0	0
Balance at Dec. 31, 2015	780,972	383,144	404,990	(7,162)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	59,106	0		211
Net income	58,895		58,895
Dividends on common stock	(51,624)	0	(51,624)	0
Stock-based compensation	2,924	2,924	0	0
Shares issued pursuant to equity based plans	6,358	6,358	0	0
Issuance of common stock, net of issuance costs	52,761	52,761	0	0
Balance at Dec. 31, 2016	$ 850,497	$ 445,187	$ 412,261	$ (6,951)