Stock-based Compensation - Summary of Share Based Compensation Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stock-based compensation expense:
Total stock-based compensation expense	$ 1,042	$ 599	$ 1,731	$ 999
Time-based restricted units [Member]
Stock-based compensation expense:
Total stock-based compensation expense	322	113	450	222
Performance-based restricted units [Member]
Stock-based compensation expense:
Total stock-based compensation expense	$ 720	$ 486	$ 281	$ 777