Earnings (Loss) Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share
Net income for basic and diluted earnings per share	$ 12,981	$ 11,365	$ 12,926	$ 13,620	$ 9,662	$ 7,715	$ 5,086	$ 8,622	$ 50,892	$ 31,085	$ (247,859)
Shares of common stock and common stock equivalents:
Average common shares used in basic computation	34,521,000	35,093,000	35,720,000	36,081,000	36,287,000	36,544,000	36,956,000	37,378,000	35,349,000	36,788,000	38,418,000
Effect of dilutive securities (in shares)									1,016,000	1,326,000
Average common shares used in diluted computation	35,640,000	36,026,000	36,641,000	37,185,000	37,685,000	37,781,000	38,000,000	38,615,000	36,365,000	38,114,000	38,418,000
Income (loss) per share:
Basic (in dollars per share)	$ 0.38	$ 0.32	$ 0.36	$ 0.38	$ 0.27	$ 0.21	$ 0.14	$ 0.23	$ 1.44	$ 0.84	$ (6.45)
Diluted (in dollars per share)	$ 0.36	$ 0.32	$ 0.35	$ 0.37	$ 0.26	$ 0.20	$ 0.13	$ 0.22	$ 1.40	$ 0.82	$ (6.45)
Anti-dilutive equity awards not included in the detailed earnings per share computation
Equity awards not included in the diluted earnings per share computation									400,000	200,000	3,600,000