Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Data - Unaudited [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	Quarter Ended
	Mar. 31		Jun. 30		Sept. 30		Dec. 31
2015
Total revenue	$	81,484	$	83,781	$	86,016	$	90,387
Gross profit	$	42,514	$	43,761	$	46,265	$	48,257
Net income	$	9,686	$	13,570	$	16,266	$	5,463
Net income per share:
Basic	$	0.62	$	0.86	$	1.02	$	0.34
Diluted	$	0.60	$	0.83	$	0.98	$	0.33
2014
Total revenue	$	73,230	$	78,677	$	77,457	$	79,896
Gross profit	$	36,027	$	37,542	$	38,147	$	39,685
Net income	$	6,657	$	5,878	$	6,428	$	7,372
Net income per share:
Basic	$	0.44	$	0.39	$	0.42	$	0.48
Diluted	$	0.43	$	0.38	$	0.42	$	0.46