Operations and Summary of Significant Accounting Policies - Revisions and Out of Period Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Out-of-period adjustments
Gross profit	$ 82,762	$ 100,341	$ 98,318	$ 77,498	$ 72,797	$ 95,553	$ 95,900	$ 77,780	$ 358,919	$ 342,030	$ 313,531
Income from operations	$ 22,485	$ 35,249	$ 35,009	$ 16,277	$ 15,320	$ 32,218	$ 32,133	19,605	109,021	99,276	81,478
Net income									$ 67,888	$ 63,531	$ 50,971
Restatement Adjustment
Out-of-period adjustments
Gross profit								2,300
Income from operations								2,000
Net income								$ 1,300