Segment information - Segment Adjusted EBITDA to Net Income (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Total segment reporting adjusted EBITDA	$ 16,251,000	$ 15,433,000
Depreciation and amortization	3,938,000	3,725,000
Interest expense, net	2,385,000	3,440,000
Gain on sale or disposition of assets and sublease	(178,000)	(143,000)
Loss on early extinguishment of debt	0	134,000
Equity-based compensation	258,000	380,000
Non-cash straight-line rent expense	147,000	339,000
Acquisition integration costs	18,000
Public offering related expenses		947,000
Income before provision for income taxes	9,683,000	5,861,000
Provision for income taxes	1,885,000	454,000
Net income	7,798,000	5,407,000
Board of Directors Chairman
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Chairman executive compensation		$ 750,000