Restatement of Previously Issued Unaudited and Audited Financial Statements - Effect of Restatement on Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Condensed Consolidated Balance Sheet Data:
Deferred income taxes	$ 70,436	$ 71,719	$ 73,292
Total assets	732,149	752,838	771,113
Other current liabilities	58,436	27,153	27,732
Total current liabilities	393,945	322,733	437,563
PEAKS Trust senior debt, excluding current portion	36,930	48,166	53,320
Total liabilities	580,518	610,766	645,185
Retained earnings	976,776	963,737	949,146
Total shareholders' equity	151,631	142,072	125,928	$ 115,646
Total liabilities and shareholders' equity	732,149	$ 752,838	$ 771,113
As Previously Reported [Member]
Condensed Consolidated Balance Sheet Data:
Deferred income taxes	66,758
Total assets	728,471
Other current liabilities	58,333
Total current liabilities	393,842
PEAKS Trust senior debt, excluding current portion	27,422
Total liabilities	570,907
Retained earnings	982,709
Total shareholders' equity	157,564
Total liabilities and shareholders' equity	728,471
Interest Method Adjustment [Member]
Condensed Consolidated Balance Sheet Data:
Deferred income taxes	3,678
Total assets	3,678
Other current liabilities	103
Total current liabilities	103
PEAKS Trust senior debt, excluding current portion	9,508
Total liabilities	9,611
Retained earnings	(5,933)
Total shareholders' equity	(5,933)
Total liabilities and shareholders' equity	$ 3,678